Wood heater with enhanced microwave choke system

ABSTRACT

A microwave heater equipped with a microwave choke and suitable for heating wood under vacuum. The microwave choke inhibits leakage of microwave energy between a door of the heater and a main vessel body of the heater without causing arcing at the choke, even at low pressures. In certain situations, the microwave choke can be configured with side-by-side choke cavities. In certain situations, the microwave choke can be removably coupled to the door and/or vessel body for easier fabrication, installation, and/or replacement.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent ApplicationNos. 61/427,030; 61/427,042; 61/427,053; 61/427,056; 61/427,064;61/427,067; 61/427,070; 61/427,072; 61/427,075; 61/427,076; 61/427,079;and 61/427,080, filed Dec. 23, 2010.

FIELD OF THE INVENTION

This invention generally relates to microwave heating systems suitablefor heating wood.

BACKGROUND

Electromagnetic radiation, such as microwave radiation, is a knownmechanism for delivering energy to an object. The ability ofelectromagnetic radiation to penetrate and heat an object both rapidlyand effectively has proven advantageous in many chemical and industrialprocesses. Further, because the use of microwave energy as a heat sourceis generally non-invasive, microwave heating is particularly useful inprocessing ‘sensitive’ dielectric materials, such as food andpharmaceuticals, and can even be useful for heating materials having arelatively poor thermal conductivity, such as wood. However, thecomplexities and nuances of safely and effectively applying microwaveenergy, especially on a commercial scale, have severely limited itsapplication in several types of industrial processes.

Because of its wide suitability for a variety of applications, itsrenewable nature, and its relatively low cost, wood is one of the mostwidely used building materials in existence. However, because wood is anatural product, its physical and structural properties can varysubstantially, not only amongst different species, but also amongstdifferent trees, or even different locations within the same piece ofwood. Further, wood is generally hygroscopic, which affects itsdimensional stability, and its biochemical composition makes itsusceptible to attack by insects and fungi. As a result, several typesof wood treatment processes have been developed to increase thestability of wood through modification of its chemical, physical, and/orstructural properties. Examples of treatment processes includeimpregnation treatments, coating treatments, thermal modification, andchemical modification. The latter two treatment processes generallyalter the properties of wood to a more drastic degree than the othersand, consequently, these types of processes typically involve morecomplex schemes and systems. For example, many chemical and thermaltreatment processes can be carried out under vacuum and/or in thepresence of one or more treatment chemicals. As a result,commercialization of these types of technologies has been limited, andmultiple challenges remain to be overcome in order for these processesto be industrialized on a wide scale.

Thus, a need exists for a more efficient and cost effectivecommercial-scale system suitable for chemically or thermally treatingwood. A need also exists for an efficient and cost effectiveindustrial-scale microwave heating system suitable for use in a widevariety of processes and applications, including the treatment of wood.

SUMMARY OF THE INVENTION

One embodiment of the present invention concerns a system for producingchemically-modified, dried, and/or thermally-modified wood, the systemcomprising a microwave heater comprising a vessel body and a door forselectively permitting and blocking passage of a bundle of wood into andout of the interior of said microwave heater. The door and the vesselbody present respective door-side and body-side sealing surfaces thatdirectly or indirectly form a fluid seal between the door and the vesselbody when the door is closed, wherein the door and the vessel bodycooperatively form at least a portion of a microwave choke effective toinhibit leakage of microwave energy out of the microwave heater betweenthe door and the vessel body when the door is closed. The microwavechoke comprises a first radially-extending choke cavity, a secondradially-extending choke cavity, and a radially-extending chokeguidewall disposed at least partly between the first and second chokecavities when the door is closed, wherein at least a portion of thesecond choke cavity extends alongside at least a portion of the firstchoke cavity when the door is closed.

Another embodiment of the present invention concerns a system forproducing chemically-modified, dried, and/or thermally-modified wood,the system comprising a microwave heater comprising a cylindrical vesselbody, a door, and a microwave choke. The microwave heater is configuredto receive and heat a bundle of wood, wherein the microwave choke isoperable to substantially prevent leakage of microwave energy out of themicrowave heater between the door and the vessel body when the door isclosed. The microwave choke comprises a removable choke portionremovably coupled to the vessel body or the door.

Still another embodiment of the present invention concerns a process forproducing chemically-modified, dried, and/or thermally-modified wood,the process comprising: (a) loading a bundle of wood into a microwaveheater through an open door of the microwave heater; (b) closing thedoor of the microwave heater to thereby form a fluid seal between thedoor and a vessel body of the microwave heater; (c) maintaining apressure of not more than 350 torr in the microwave heater; (d) heatingthe bundle of wood with microwave energy introduced into the microwaveheater while the vacuum is maintained; and (e) simultaneously with step(d), using a microwave choke to prevent at least a portion of themicrowave energy from exiting the microwave heater at the junction ofthe door and the vessel body.

Yet another embodiment of the present invention concerns a process forproducing chemically-modified, dried, and/or thermally-modified wood,the process comprising: (a) attaching a removable choke portion to adoor or a vessel body of a microwave heater; (b) heating a bundle ofwood with microwave energy introduced into the microwave heater; and (c)simultaneously with step (b), using a microwave choke to prevent atleast a portion of the microwave energy from exiting the microwaveheater at a junction of the door and the vessel body, wherein themicrowave choke comprises the removable choke portion.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments of the present invention are described in detailbelow with reference to the attached drawing figures, wherein:

FIG. 1 is a top view of a wood treatment system configured in accordancewith one embodiment of the present invention, particularly illustratinga rail system for transporting bundles of wood to and from a chemicalmodification reactor and a wood heater;

FIG. 2 is a top view of a wood treatment system configured in accordancewith an alternative embodiment of the present invention, particularlyillustrating a turntable system for transporting bundles of wood to andfrom a plurality of chemical modification reactors and a plurality ofwood heaters;

FIG. 3 is a top view of a wood treatment system configured in accordancewith an alternative embodiment of the present invention, particularlyillustrating a roller system for transporting bundles of wood to andfrom a plurality of chemical modification reactors and a plurality ofwood heaters;

FIG. 4 a is a top view of a pass-through wood treatment system suitablefor use in producing chemically-modified wood and configured inaccordance with one embodiment of the present invention, particularlyillustrating a chemical modification reactor and a wood heater thatcomprise separate, axially-aligned, two-door vessels and include a vaporcontainment room located between the reactor and heater vessels;

FIG. 4 b is an isometric view of the pass-through wood treatment systemof FIG. 4 a, particularly illustrating an exemplary blast panel/wall ofthe vapor containment room;

FIG. 4 c is a sectional view of the vapor containment room depicted inFIGS. 4 a and 4 b, particularly illustrating an exemplary pair ofone-way vents for allowing fluid (e.g., air) from the externalenvironment to flow into the vapor containment room;

FIG. 4 d is a side view of the pass-through wood treatment system ofFIG. 4 a, but also illustrating a ventilation system for drawing vaporsand gasses in through the vapor containment room and in through aproduct vapor removal structure located at the outlet of the heater;

FIG. 5 is a schematic view of a microwave heating system configured inaccordance with one embodiment of the present invention, particularlyillustrating a microwave heater that is equipped with a vacuum systemand receives microwave energy from a microwave generator via a microwavedistribution system;

FIG. 6 is an isometric view of a two-door, pass-through vessel suitablefor use as a chemical modification reactor and/or microwave heater inaccordance with various embodiments of the present invention,particularly illustrating the shape and dimensional proportions of thevessel;

FIG. 7 a is a partial sectional view of the junction of a door flangeand a vessel flange of a microwave heater configured in accordance withone embodiment of the present invention, particular illustrating amicrowave choke cooperatively formed by the door and vessel flanges andhaving two chambers that extend parallel to and alongside one another;

FIG. 7 b is a partial sectional view of a microwave choke similar thechoke depicted in FIG. 7 a, but having choke cavities that extend at anacute angle relative to one another;

FIG. 7 c is a cut-away isometric view of the door flange of a microwaveheater equipped with the microwave choke configuration depicted in FIG.7 a, particularly illustrating a plurality of circumferentially-spaced,open-ended slots or gaps formed in a guidewall of the choke;

FIG. 7 d is a side view of an open door on a microwave heater equippedwith a microwave choke having a removable portion configured inaccordance with one embodiment of the present invention, particularlyillustrating that the removable portion of the microwave choke comprisesa plurality of individually removable and replaceable choke segments;

FIG. 7 e is a sectional view of a “G”-shaped removable choke portionpreviously depicted in FIG. 7 d;

FIG. 7 f is a sectional view of a “J”- or “U”-shaped removable chokeportion configured in accordance with a first alternative embodiment ofthe present invention;

FIG. 7 g is a sectional view of an “L”-shaped removable choke portionconfigured in accordance with a second alternative embodiment of thepresent invention;

FIG. 7 h is a sectional view of an “I”-shaped removable choke portionconfigured in accordance with a third alternative embodiment of thepresent invention;

FIG. 8 a is a cut-away isometric view of a microwave heater configuredin accordance with one embodiment of the present invention, particularlyillustrating the heater as being equipped with an elongated waveguidelauncher having staggered launch openings on opposite sides of thelauncher;

FIG. 8 b is an enlarged partial view of the waveguide launcher depictedin FIG. 8 a, particularly illustrating the configuration of the launchopenings and the thickness of the sidewalls defining the launchopenings;

FIG. 9 a is a side view of a microwave heating system configured inaccordance with one embodiment of the present invention, particularlyillustrating a microwave distribution system for delivering microwaveenergy to the microwave heater;

FIG. 9 b is a top cut-away view of the microwave heater depicted in FIG.9 a, particularly illustrating the microwave distribution system asincluding one pair of TM_(ab) launchers on one side of the microwaveheater and a second pair of the TM_(ab) launchers on the opposite sideof the microwave heater;

FIG. 9 c is a diagram illustrating what is meant by the terms “oppositeside” and “same side”;

FIG. 9 d is a diagram illustrating what is meant by the term “axiallyaligned”;

FIG. 9 e is a partial cut-away isometric view of a microwave launchingand reflecting or dispersing system configured in accordance with oneembodiment of the present invention, particularly illustrating a launchsystem similar to that depicted in FIG. 9 b but also including a movablereflector associated with each microwave launcher;

FIG. 9 f is an isometric view of one embodiment of a reflector suitablefor use in a microwave heating system as described herein, particularlyillustrating the reflector as having a non-planar reflecting surfacewith a concavity of a first configuration;

FIG. 9 g is an isometric view of another embodiment of a reflectorsuitable for use in a microwave heating system described herein,particularly illustrating the reflector as having a non-planarreflecting surface with a concavity of a second configuration;

FIG. 9 h is a side elevation view of one embodiment of a reflectorsuitable for use in a microwave heating system described herein,particularly illustrating the curvature of the reflector surface;

FIG. 9 i is an enlarged, cut-away, isometric view of a microwavelauncher and reflector pair previously depicted in FIG. 9 e,particularly illustrating an actuator system for providing oscillatingmovement of the reflector;

FIG. 10 a is a side view of a microwave heating system configured inaccordance with one embodiment of the present invention, particularlyillustrating a microwave distribution system equipped with a pluralityof TM_(ab) barrier assemblies;

FIG. 10 b is an axial sectional view of one of the TM_(ab) barrierassemblies depicted in FIG. 10 a, particularly illustrating the barrierassembly as having two floating, sealed windows and impedancetransforming diameter step-changes near the junction of the barrierassembly and the waveguides between which the barrier assembly iscoupled;

FIG. 10 c is an end view of the microwave heating system depicted inFIG. 10 a with a bundle of wood being received in the interior of themicrowave heater, particularly illustrating the microwave heater asbeing equipped with split microwave launchers on opposite sides of theheater and movable reflectors for rastering microwave energy emittedfrom the split launchers;

FIG. 10 d is an enlarged side view of one of the split launchersdepicted in FIG. 10 c, particularly illustrating the launch angle forthe two separate microwave energy fractions emitted from the splitlauncher;

FIG. 10 e is an enlarged view of one embodiment of a system for moving areflector, particularly illustrating an actuator used to causeoscillation of the reflector and a bellows for inhibiting fluid leakageat the location where the actuator penetrates the wall of the microwaveheater;

FIG. 11 a is a schematic top view of a microwave heating systemconfigured in accordance with one embodiment of the present invention,particularly illustrating the heating system as including a plurality ofmicrowave switches for routing microwave energy to different microwavelaunchers in an alternating fashion;

FIG. 11 b is a schematic view of a microwave heating system configuredin accordance with an alternative embodiment of the present invention,particularly illustrating the heating system as including a plurality ofmicrowave switches for routing microwave energy to different microwavelaunchers in an alternating fashion;

FIG. 12 a presents results of a computer simulation predicting electricfield strengths proximate a door and body flange of a microwave vesselthat does not comprise a microwave choke;

FIG. 12 b presents results of a computer simulation predicting electricfield strengths proximate a door and body flange of a microwave vesselthat does include a microwave choke, particularly illustrating theability of the choke to prevent or substantially minimize microwaveleakage from the vessel;

FIG. 13 is a schematic representation of a bundle of wood, particularlyillustrating the configuration utilized when determining interiorsurface temperatures as described in Example 3;

FIG. 14 is a cumulative frequency histogram incorporating thermal dataobtained from surfaces B′ through D′ of the composite bundle shown inFIG. 13; and

FIG. 15 is a cumulative frequency histogram illustrating a predictedtemperature distribution resulting from extrapolated thermal data for abundle of acetylated wood as described in Example 4.

DETAILED DESCRIPTION

In accordance with one embodiment of the present invention, a heatingsystem is provided. Heating systems configured according to variousembodiments of the present invention can comprise a heat source, aheating vessel (e.g., a heater), and an optional vacuum system.Typically, heating systems configured according to one embodiment of thepresent invention can be suitable for use as stand-alone heating units,or can be employed as, or in conjunction with, chemical reactors in avariety of processes. Heating systems configured according to severalembodiments of the present invention will now be described in detailbelow, with reference to the Figures.

In one embodiment, a heating system of the present invention can be usedto heat lignocellulosic materials. Lignocellulosic materials can includeany material comprising cellulose and lignin and, optionally, othermaterials such as hemicelluloses. Examples of lignocellulosic materialscan include, but are not limited, to wood, bark, kenaf, hemp, sisal,jute, crop straws, nutshells, coconut husks, grass and grain husks andstalks, corn stover, bagasse, conifer and hardwood barks, corn cobs, andother crop residuals, and any combination thereof.

In one embodiment, the lignocellulosic material can be wood. The woodcan be a softwood or a hardwood. Examples of suitable wood species caninclude, but are not limited to, pine, fir, spruce, poplar, oak, maple,and beech. In one embodiment, wood can comprise red oak, red maple,German beech, or Pacific albus. In another embodiment, the wood cancomprise a pine species including, for example, Radiata pine, Scotspine, Loblolly pine, Longleaf pine, Shortleaf pine, or Slash pine, thelatter four of which can be collectively referred to as “Southern YellowPine.” The wood processed by heating systems according to one embodimentof the present invention can be in any suitable form. Non-limitingexamples of suitable forms of wood can include, but are not limited to,shredded wood, wood fibers, wood flour, wood chips, wood particles, woodflakes, wood strands, and wood excelsior. In one embodiment, the woodprocessed in one or more heating systems of the present invention cancomprise sawn timber, debarked tree trunks or limbs, boards, planks,veneers, beams, profiles, squared timber, or any other cut of lumber.

Typically, the size of the wood can be defined by two or moredimensions. The dimensions can be actual “measured” dimensions or can benominal dimensions. As used herein, the term “nominal dimension” refersto the dimensions calculated using the size designation for the wood.The nominal size can be larger than the measured dimensions. Forexample, a dried “2×4” can have actual dimensions of 1.5 inches by 3.5inches, but the nominal dimensions of “2×4” are still used. It should beunderstood that the dimensions referred to herein are generally nominaldimensions, unless otherwise noted.

In one embodiment, the wood can have three dimensions: a length, orlongest dimension; a width, or second longest dimension; and athickness, or shortest dimension. Each of the dimensions can besubstantially the same, or, one or more of the dimensions can bedifferent from one or more of the other dimensions. According to oneembodiment, the length of the wood can be at least about 6 inches, atleast about 1 foot, at least about 3 feet, at least about 4 feet, atleast about 6 feet, or at least about 10 feet. In another embodiment,the width of the wood can be at least about 0.5 inches, at least about 1inch, at least about 2 inches, at least about 4 inches, at least about 8inches, at least about 12 inches, or at least about 24 inches and/or nomore than about 10 feet, no more than about 8 feet, no more than about 6feet, no more than about 4 feet, no more than about 3 feet, no more thanabout 2 feet, no more than about 1 foot, or no more than about 6 inches.In yet another embodiment, the thickness of the wood can be at leastabout 0.25 inches, at least about 0.5 inches, at least about 0.75inches, at least about 1 foot, at least about 1.5 feet, or at leastabout 2 feet and/or no more than about 4 feet, no more than about 3feet, no more than about 2 feet, no more than about 1 foot, and/or nomore than about 6 inches.

According to one embodiment, the wood can comprise one or more pieces ofsolid wood, engineered solid wood, or a combination thereof. As usedherein, the term “solid wood” refers to wood that measures at leastabout 10 centimeters in at least one dimensions but that is otherwise ofany dimension (e.g., lumber having dimensions as described previously).As used herein, the term “engineered solid wood” refers to a wooden bodyhaving the minimum dimensions of solid wood (e.g., at least onedimension of at least about 10 cm), but that is formed of smaller bodiesof wood and at least one binder. The smaller bodies of wood inengineered solid wood may or may not have one or more of the dimensionsdescribed previously with respect to solid wood. Non-limiting examplesof engineered solid wood can include wood laminates, fiberboard,oriented strand board, plywood, wafer board, particle board, andlaminated veneer lumber.

In one embodiment, the wood can be grouped in a bundle. As used herein,the term “bundle” refers to two or more pieces of wood stacked, placed,and/or fastened together in any suitable fashion. According to oneembodiment, a bundle can comprise a plurality of boards stacked andcoupled to one another via a belt, strap, or other suitable device. Inone embodiment, the two or more pieces of wood can be in direct contactor, in another embodiment, the wood pieces can be at least partiallyspaced using at least one spacer or “sticker” disposed therebetween.

In one embodiment, the bundle can have any suitable dimensions and/orshape. In one embodiment, the bundle can have a total length, or longestdimension, of a least about 2 feet, at least about 4 feet, at leastabout 8 feet, at least about 10 feet, at least about 12 feet, at leastabout 16 feet, or at least about 20 feet and/or no more than about 60feet, no more than about 40 feet, or no more than about 25 feet. Thebundle can have a height, or second longest dimension, of at least about1 foot, at least about 2 feet, at least about 4 feet, at least about 6feet, at least about 8 feet, and/or no more than about 16 feet, no morethan about 12 feet, no more than about 10 feet, no more than about 8feet, no more than about 6 feet, or no more than about 4 feet. In oneembodiment, the bundle can have a width, or shortest dimension, of atleast about least about 1 foot, at least about 2 feet, at least about 4feet, at least about 6 feet, and/or no more than about 20 feet, no morethan about 16 feet, no more than about 12 feet, no more than about 10feet, no more than about 8 feet, or no more than about 6 feet. The totalvolume of the bundle, including the spaces between the boards, if any,can be at least about 50 cubic feet, at least about 100 cubic feet, atleast about 250 cubic feet, at least about 375 cubic feet, or at leastabout 500 cubic feet. According to one embodiment, the weight of thebundle of wood (or cumulative weight of one or more objects, articles,or loads to be treated) introduced into the reactor and/or heater of oneor more heating systems of the present invention (e.g., prior to heatingor treatment) can be at least about 100 pounds, at least about 500pounds, at least about 1,000 pounds, or at least about 5,000 pounds. Inone embodiment, the bundle can be cubical or cuboidal in shape.

In another embodiment, one or more heating systems of the presentinvention can be used to chemically modify, dry, and/or thermally modifywood, thereby producing chemically-modified, dried, and/orthermally-modified wood. Wood that has been dried and/orthermally-modified wood may referred to as “thermally-treated” wood,such that the term “thermally-treated wood” refers to wood that has beenheated, dried, and/or thermally-modified. As used herein, the term“thermally modify” means to at least partially modify the chemicalstructure of at least a portion of one or more pieces of wood in theabsence of an exogenous treating agent. In one embodiment, a heatingsystem, specific configurations of which will be described in detailshortly, can be used to heat and/or dry wood in a thermal modificationprocess to thereby provide a bundle of thermally-modified wood.According to one embodiment, thermal modification can occursimultaneously with heating and/or drying of wood in a wood heaterand/or dryer, while, in another embodiment, wood can be heated and/ordried in a wood heater or dryer without being thermally modified. Asused herein, the term “dry” means to cause or accelerate vaporization ofor to otherwise remove at least a portion of one or more liquid orotherwise heat-removable components from the wood via the addition ofheat or other suitable form of energy. Thermal modification processescan include a step of contacting wood with one or more heat transferagents such as, for example, steam, heated inert vapors like nitrogen orair, or even liquid heat transfer media such as heated oils. In anotherembodiment, a radiant heat source may be used during thermalmodification. Thermally-modified wood can have a substantially lowermoisture content than untreated wood and can have enhanced physicaland/or mechanical properties such as, for example, increasedflexibility, higher resistance to decay and biological attacks, andincreased dimensional stability.

In yet another embodiment, heating systems configured according tovarious embodiments of the present invention can be used to chemicallymodify wood. As used herein, the term “chemically modify” means to atleast partially modify the chemical structure of at least a portion ofone or more pieces of wood in the presence of one or more exogenoustreating agents. Specific types of chemical modification processes caninclude, but are not limited to, acetylation and other types ofesterification, epoxidation, etherification, furfurlyation, methylation,and/or melamine treatment. Non-limiting examples of suitable treatmentagents can include anhydrides (e.g., acetic, phthalic, succinic, maleic,propionic, or butyric); acid chlorides; ketenes; carboxylic acids;isocyanates; aldehydes (e.g., formaldehyde, acetyldehyde, ordifunctional aldehydes); chloral; dimethyl sulfate; alkyl chlorides;beta-propiolacetone; acrylonitrile; epoxides (e.g., ethylene oxide,propylene oxide, or butylenes oxides); difunctional epoxides; borates;acrylates; silicates; and combinations thereof.

Processes for chemically modifying wood can include a chemicalmodification step followed by a heating step. During the chemicalmodification or reaction step, which can be carried out in a chemicalmodification reactor, wood can be exposed to one or more of theexogenous treatment agents described previously, which can react with atleast a portion of the functional groups (e.g., hydroxyl groups) of theuntreated wood to thereby provide chemically-modified wood. During thechemical modification step, one or more heat-initiated chemicalreactions can take place, which may or may not be initiated by anexternal source of energy (e.g., thermal energy or electromagneticenergy, including, for example, microwave energy.) Specific details ofchemical modification processes vary amongst the many types of chemicalmodification, but most chemically-modified wood can have enhancedstructural, chemical, and/or mechanical properties including lowermoisture sorption, higher dimensional stability, more biological andpest resistance, increased decay resistance, and/or higher weatherresistance as compared to untreated wood.

In one embodiment, wood can be acetylated in a wood acetylation reactor.Acetylation can include replacement of surface or near-surface hydroxylgroups with acetyl groups. In one embodiment, the treatment agentutilized during acetylation can comprise acetic anhydride in aconcentration of at least about 50 weight percent, at least about 60weight percent, at least about 70 weight percent, at least about 80weight percent, at least about 90 weight percent, at least about 98weight percent, or about 100 weight percent, with the balance, if any,comprising acetic acid and/or one or more diluents or optionalacetylation catalysts. In one embodiment, the treatment agent foracetylation can comprise mixtures of acetic acid and acetic anhydridehaving an anhydride-to-acid weight ratio of at least about 80:20, atleast about 85:15, at least about 90:10, or at least about 95:5.

Prior to acetylation, the wood can be dried to reduce its moisture(e.g., water) content to no more than about 25 weight percent, no morethan about 20 weight percent, no more than about 15 weight percent, nomore than about 12 weight percent, no more than about 9 weight percent,or no more than about 6 weight percent using kiln drying, vacuumdegassing, or other suitable methods. During acetylation, the wood canbe contacted with the treatment agent via any suitable method. Examplesof suitable contact methods can include, but are not limited to, vaporcontacting, spraying, liquid immersion, or combinations thereof. In oneembodiment, the temperature of the treatment vessel can be no more thanabout 50° C., no more than about 40° C., or no more than about 30° C.,while the pressure can be at least about 25 psig, at least about 50psig, at least about 75 psig and/or no more than about 500 psig, no morethan about 250 psig, or no more than about 150 psig during the time thewood is contacted with the treatment agent.

Once the contacting step is complete, at least a portion of the liquidtreatment agent, if present, can optionally be drained from the reactorand heat can be added to initiate and/or catalyze the reaction. In oneembodiment, microwave energy, thermal energy, or combinations thereofcan be introduced into the vessel in order to increase the temperatureof the wood to at least about 50° C., at least about 65° C., at leastabout 80° C. and/or to no more than about 175° C., no more than about150° C., or no more than about 120° C., while maintaining a pressure inthe reactor of at least about 750 torr, at least about 1,000 torr, atleast about 1,200 torr, or at least about 2,000 torr and/or no more thanabout 7,700 torr, no more than about 5,000 torr, no more than about3,500 torr, or no more than about 2,500 torr. According to oneembodiment, least a portion of the heat added to the reactor can betransferred to the wood from a non-microwave source, such as, forexample, a hot vapor stream comprising at least about 50, at least about75, at least about 90, or at least about 95 weight percent acetic acid,with the balance comprising acetic anhydride and/or diluents. In oneembodiment, the hot vapor, a portion of which can condense on at least aportion of the bundle of wood being treated, is introduced into thereaction vessel for at least about 20 minutes, at least about 35 minutesor, at least about 45 minutes and/or no more than about 180 minutes, nomore than about 150 minutes, or no more than about 120 minutes.

After the reaction step, the “chemically-wet” chemically-modified woodcan comprise at least one chemical component capable of being removed byheat and/or vaporization. As used throughout this application, the terms“chemically-wet” or “chemical-wet” refers to wood containing one or morechemicals present at least partially in a liquid phase as a result of achemical treatment or modification. A “chemically-wet” bundle of woodcan refer to a bundle of wood of which at least a portion is at leastpartially chemically-wet. Some examples of the one or more chemicals caninclude reactants, impregnants, reaction products, or the like. Forexample, when wood is acetylated, at least a portion of the residualacetic acid and/or anhydride can be removed by vaporization. As usedherein, the term “acid-wet” refers to wood containing residual aceticacid and/or anhydride. An “acid-wet” bundle of wood refers to a bundleof wood of which at least a portion is at least partially acid-wet.According to one embodiment of the present invention, the chemical-wetor acid-wet wood can comprise at least about 20 weight percent, at leastabout 30 weight percent, at least about 40 weight percent, or at leastabout 45 weight percent and/or no more than about 75 weight percent, nomore than about 60 weight percent, or no more than about 50 weightpercent of one or more heat-removable or vaporizable chemicals, such as,for example, acetic acid and/or anhydride. As used herein, the term“heat-removable” or “vaporizable” chemical component refers to acomponent that can be removed by heat and/or vaporization. In oneembodiment, the vaporizable or heat-removable component or chemical cancomprise acetic acid.

At least a portion of one or more heat-removable chemicals can then beremoved via flash vaporization from the chemical-wet wood. In oneembodiment, the flash vaporization step can be accomplished by reducingthe pressure in the reactor from a pressure of at least about 1,000torr, at least about 1,200 torr, at least about 1,800 torr, or at leastabout 2,000 torr and/or no more than about 7,700 torr, no more thanabout 5,000 torr, no more than about 3,500 torr, no more than about2,500 torr, or no more than about 2,000 torr to atmospheric pressure. Inanother embodiment, the flash vaporization step can be accomplished byreducing the pressure of the reactor from an elevated pressure, asdescribed above, or atmospheric pressure, to a pressure of no more thanabout 100 torr, no more than about 75 torr, no more than about 50 torr,or no more than about 35 torr. According to one embodiment, the amountof one or more heat-removable chemical components (e.g., the chemicalcontent) remaining in the chemical-wet wood after the flash vaporizationstep can be at least about 6 weight percent, at least about 8 weightpercent, at least about 10 weight percent, at least about 12 weightpercent, or at least about 15 weight percent and/or no more than about60 weight percent, no more than about 40 weight percent, no more thanabout 30 weight percent, no more than about 25 weight percent, no morethan about 20 weight percent, or no more than about 15 weight percent.

According to one embodiment, a heating step can be carried outsubsequent to the chemical modification step to further heat and/or drythe chemically-modified (or chemical-wet) wood to thereby provide aheated and/or dried bundle of chemically-modified wood. As used herein,a bundle or other article or material is referred to as “heated” simplyas a convenience to indicate that a temperature of at least a portion ofthe bundle has been elevated above ambient temperature. Similarly, asused throughout this application, a bundle or other article or materialis referred to as “dried” simply as a convenience to indicate that atleast some heat-removable chemicals have been removed from at least aportion of the bundle by, in some embodiments, heating. In oneembodiment, the heating step can be operable to further reduce the levelof one or more heat-removable chemical components present in the wood.The energy source utilized during the heating step can be any source ofradiative, conductive, and/or convective energy suitable for heatingand/or drying wood. In one embodiment, the heater can be a microwaveheater employing a microwave energy. In another embodiment, another heatsource can be utilized to directly or indirectly (via, for example, ahot gas injection, a jacketed or heat-traced vessel, or other means)heat at least a portion of the vessel, such as, for example, one or moreside walls. In this embodiment, the side walls can be heated to atemperature of at least about 45°, at least about 55° C., or at leastabout 65° C. and/or not more than about 115° C., not more than about105° C., or not more than about 95° C. The heating step can be carriedout under any suitable conditions, including pressures above, at, ornear atmospheric pressure. Specific embodiments of various heatingsystems suitable for use in producing chemically-modified and/orthermally-modified wood will be discussed in detail shortly.

The heating step can be carried out such that at least about 50 percent,at least about 65 percent, at least about 75 percent, or at least about95 percent of the total amount of the one or more heat-removablechemical components remaining in the chemical-wet wood is removed. Inone embodiment, this can correspond to at least about 100 pounds, atleast about 250 pounds, at least about 500 pounds, or at least about1,000 pounds of total liquid removed. As a result of the heating step,in one embodiment, the heated or dried chemically-modified wood cancomprise no more than about 5 weight percent, no more than about 4weight percent, no more than about 3 weight percent, no more than about2 weight percent, or no more than about 1 percent, based on the initial(pre-heated) weight of the bundle, of the one or more heat-removablechemicals (e.g., acetic acid). In addition, the heated or driedchemically-modified wood can have a water content of no more than about6 weight percent, no more than about 5 weight percent, no more thanabout 3 weight percent, no more than about 2 weight percent, or no morethan about 1 weight percent, or no more than about 0.5 weight percentbased on the initial (pre-heated) weight of the wood. In one embodiment,the wood can have a water content of approximately 0 percent subsequentto the heating step.

In one embodiment, the chemical modification step and the heating stepcan take place in a single vessel. In another embodiment, the chemicalmodification step and the heating step can be carried out in separatevessels, such that the internal volumes of the chemical modificationreactor and the heater are locationally distinct. As used herein, the“internal volume” of a vessel refers to the entirety of the spaceencompassed by the vessel, including any volume defined by or within thedoor or doors of the vessel when closed. As used herein, the term“locationally distinct” means that the internal volumes are notoverlapping. When the chemical modification reactor and heater compriseseparate vessels, various types of wood transportation systems can beutilized in order to transport the wood between the two vessels. In oneembodiment, the transportation system can comprise rails (as illustratedin FIG. 1), tracks, belts, hooks, rollers (as illustrated in FIG. 3),bands, carts, motorized vehicles, fork trucks, pulleys, turntables (asillustrated in FIG. 2), and any combination thereof. Various embodimentsof wood treatment facilities capable of producing chemically-modifiedand/or thermally-modified wood will now be discussed in detail, withrespect to FIGS. 1-3.

Referring now to FIG. 1, one embodiment of a wood treatment facility 10is illustrated as comprising a chemical modification system 20, aheating system 30, a transportation system 40, and raw and finishedmaterial storage areas 60 a,b. Chemical modification system 20 comprisesa chemical modification reactor 22, a reactor heating system 24, and anoptional reactor pressurization/depressurization system 26. Heatingsystem 30 comprises a heater 32, an energy source 34, and an optionalheater pressurization/depressurization system 36. Transportation system40 comprises a plurality of transport segments 42 a-e for transportingwood between storage areas 60 a,b, reactor 22, and heater 32, asdescribed in detail below.

In operation, one or more bundles of wood can be removed from rawmaterial storage area 60 a via transport segment 42 a. Althoughillustrated in FIG. 1 as comprising tracks or rails, it should beunderstood that transport segment 42 a can comprise any type oftransportation mechanism suitable for moving wood between storage area60 a and reactor 22. As shown in FIG. 1, the wood can then be introducedor loaded into reactor 22 via an open reactor entrance door 28.Thereafter, first reactor entrance door 28 can be closed in order toallow the wood disposed within reactor 22 to be chemically-modifiedaccording to one or more processes described above.

Once the reaction is complete, the chemical-wet wood can be withdrawnfrom reactor 22 and be transported to heater 32. According to oneembodiment, the chemical-wet wood can be removed from reactor 22 viareactor entrance door 28 and transported to heater 32 via transportsegment 42 b. In another embodiment, the wood can be removed via anoptional reactor exit door 29 and transported to heater 32 via transportsegment 42 c, as shown in FIG. 1. The chemical-wet wood can then beintroduced or loaded into heater 32 via an open heater entrance door 38,which can then be closed to thereby form a fluid seal between heaterentrance door 38 and the body of heater 32 prior to initiating theheating of the wood. When optional reactor and heater exit doors 29, 39,are present, exit doors 29, 39 can be located on generally opposite endsof reactor 22 and heater 32 than respective reactor and heater entrancedoors 28, 38.

In various embodiments, during the heating of the wood within heater 32,pressurization system 36 can be used to maintain a pressure withinheater 32 of no more than about 550 torr, no more than about 450 torr,no more than about 350 torr, no more than about 250 torr, no more thanabout 200 torr, no more than about 150 torr, no more than about 100torr, or no more than about 75 torr. In one embodiment, the vacuumsystem can be operable to reduce the pressure in heater 32 to no morethan about 10 millitorr (10⁻³ torr), no more than about 5 millitorr, nomore than about 2 millitorr, no more than about 1 millitorr, no morethan about 0.5 millitorr, or no more than about 0.1 millitorr. Inaddition, when heater 32 comprises a microwave heater, one or morefeatures described in detail shortly, including for example, an optionalmicrowave choke, one or more microwave launchers, and the like can beused to introduce energy into the interior of heater 32, thereby heatingand/or drying at least a portion of the bundle of wood containedtherein.

According to one embodiment, the wood treatment facility 10 can comprisemultiple reactors and/or heaters. Any number of reactors and/or heaterscan be employed, and the reactors and/or heaters can be arranged in anysuitable configuration. For example, wood treatment facility 10 canutilize at least 1, at least 2, at least 3, at least 5 and/or no morethan 10, no more than 8, or no more than 6 reactors and/or heaters. Whenmultiple reactors and/or heaters are employed, the vessels can be pairedin any suitable combination or ratio. For example, the ratio of reactorsto heaters can be 1:1, 1:2, 2:1, 1:3, 3:1, 2:3, 3:2, 1:4, 4:1, 4:2, 2:4,3:4, 4:3 or any feasible combination. According to one embodiment, oneor more of reactors and/or heaters can comprise separate entrance andexit doors, while, in another embodiment, one or more of the reactorsand/or heaters can comprise a single door for loading and unloadingwood. In one embodiment, the heated and/or dried wood can be removedfrom heater 34 via heater entrance door 38, and transported to storagearea 60 b via transport segment 42 d. Alternatively, the wood can bewithdrawn via an optional heater exit door 39, if present, andtransported via segment 42 e to storage area 60 b, as illustrated inFIG. 1. Various configurations of wood treatment facilities employingmultiple reactors and heaters configured according to severalembodiments of the present invention will be described briefly withrespect to FIGS. 2 and 3.

Turning now to FIG. 2, a wood treatment facility 110 configuredaccording to one embodiment of the present invention is illustrated.Wood treatment facility 110 comprises a plurality of reactorsillustrated as 122 a, 122 b, 122 n and plurality of heaters illustratedas 132 a, 132 b, 132 n. According to one embodiment, each of thereactors 122 a, 122 b, 122 n and each of the heaters 132 a, 132 b, 132 ncomprise a single door 128 a, 128 b, 128 n, 138 a, 138 b, 138 n, forselectively permitting the passage of wood into and out of each vessel.In addition, wood treatment facility 110 can comprise a rotatableplatform (illustrated as a turntable 140) operable to position a bundleof wood 102 such that it can be transported between reactors 122 a, 122b, 122 n, heaters 132, 132 b, 132 n, and a storage area 160, in variousdirections generally indicated by arrows 190 a-c.

Referring now to FIG. 3, another embodiment of a wood treatment facility210 is shown as comprising a plurality of chemical modification reactorsillustrated as 222 a, 222 n and a plurality of heaters illustrated as232 a, 232 b, 232 n. As shown in FIG. 3, each of the reactors comprisesa respective reactor entrance door 228 a, 228 n and an optional reactorexit door 229 a, 229 n. Similarly, each of the heaters 232 a, 232 b, 232n comprises a heater entrance door 238 a, 238 b, 238 n and an optionalheater exit door 239 a, 239 b, 239 n. Transportation system 240 shown inFIG. 3 comprises a plurality of segments 242 a-j and 244 a-e operable totransport wood to, from, and between reactors 222 a, 222 n and heaters232 a, 232 b, 232 n. Although illustrated as comprising continuous beltsegments, transportation system 240 can comprise one or more segmentscomprising any suitable transportation mechanism, as discussed in detailpreviously.

According to one embodiment, in operation, wood loaded into firstreactor 222 a via transport segment 242 a can be introduced throughreactor entrance door 228 a. Once the chemical modification process iscomplete, chemical-wet wood can be removed from reactor 222 a viareactor entrance door 228 a and can subsequently be transported to oneof heaters 232 a, 232 b, or 232 n via respective transport segments 242e, 242 f, 242 g. In an alternative embodiment, wood removed from reactor222 a can be removed through reactor exit door 229 a via transportsegment 244 a prior to being transported to heater 232 a, 232 b, or 232n as described previously. In addition, wood treated in reactor 222 ncan be loaded, chemically-modified, and transported to one of heaters232 a, 232 b, 232 n, in a similar manner as previously described.

Thereafter, the bundle or bundles of chemically-wet wood transported toheaters 232 a, 232 b, and 232 n can be heated and/or dried according toone or more methods described herein. In one embodiment, at least one ofheaters 232 a, 232 b, and 232 n can comprise a microwave heater. Oncethe heating step is completed, heated and/or dried bundles can bewithdrawn from heaters 232 a, 232 b, and 232 n via respective entrancedoors 238 a, 238 b, 238 n, or, optionally, from respective exit doors239 a, 239 b, 239 n, when present. Subsequently, the modified bundlescan be transported to subsequent processing and/or or storage viatransport segments 242 h,i,j or 244 c,d,e, depending on whether thebundles were removed from heater entrance doors 238 a, 238 b, 238 n orheater exit doors 239 a, 239 b, 239 n.

The chemical modification process previously discussed can be carriedout at any suitable scale. For example, the above-described woodtreatment facilities can comprise lab-scale, pilot plant-scale, orcommercial-scale wood treatment facilities. In one embodiment, the woodtreatment facility used to produce chemically-modified and/orthermally-modified wood can be a commercial-scale facility having anannual production capacity of at least about 500,000 board feet, atleast about 1 million board feet, at least about 2.5 million board feet,or at least about 5 million board feet. As used herein, the term “boardfeet” refers to a volume of wood expressed in units measuring 144 cubicinches. For example, a board having dimensions of 2 inches by 4 inchesby 36 inches has a total volume of 288 cubic inches, or 2 board feet. Invarious embodiments, the internal volume of a single chemicalmodification reactor (i.e., the “internal reactor volume”) and/or theinternal volume of a single heater (i.e., the “internal heater volume”)can be at least about 100 cubic feet, at least about 500 cubic feet, atleast about 1,000 cubic feet, at least about 2,500 cubic feet, at leastabout 5,000 cubic feet, or at least about 10,000 cubic feet in order toaccommodate commercial-scale operation.

Even when carried out on a commercial scale, chemical and/or thermalmodification processes as described herein can be carried out withrelatively short overall cycle times. For example, according to oneembodiment, the total cycle time of the chemical and/or thermalmodification processes carried out using one or more systems of thepresent invention, measured from the time the modification step isinitiated to the time the heating step is completed, can be no more thanabout 48 hours, no more than about 36 hours, no more than about 24hours, or no more than about 12 hours, no more than about 10 hours, nomore than about 8 hours, or no more than about 6 hours. This is incontrast to many conventional wood treatment processes, which can haveoverall cycle times that last several days or even weeks.

In accordance with one embodiment of the present invention, woodtreatment facilities of the present invention can comprise one or morevapor containment rooms and/or ventilation structures for substantiallyisolating the external environment (i.e., the environment immediatelyoutside the chemical modification reactor and the heater) from thechemically-wet chemically-modified wood during transport of the wood.The vapor containment rooms and/or ventilation structures can beconnected to a ventilation system that removes at least a portion of thegaseous environment out of the containment/ventilation area, therebyminimizing leakage one or more undesirable vapor-phase chemicals intothe external environment. Additional details and one embodiment of awood treatment facility employing vapor containment rooms and/orventilation structures will now be described in greater detail withrespect to FIGS. 4 a-d.

FIG. 4 a is a top view of a vapor containment room 360 coupled to achemical modification reactor 322 and a heater 332. Vapor containmentroom 360 can be operable to partially, or almost completely, isolate theexternal environment from a chemically-modified bundle of wood as thewood is transported from chemical modification reactor 322 to heater 332via a transfer region 361 located between reactor 322 and heater 332. Asused herein, the term “isolate” refers to the inhibition of fluidcommunication between one or more areas, zones, or regions. According toone embodiment, vapor containment room 360 can be coupled to aventilation system (not shown in FIG. 4 a) operable to remove at least aportion of the vapor and gases from the interior of vapor containmentroom 360, thereby reducing, minimizing, or preventing leakage of one ormore heat-removable chemical components contained within the interior ofreactor 322, within the interior of heater 332, and/or from thechemically-modified bundle of wood to the external environment.

In one embodiment, chemical modification reactor 322 can comprise areactor entrance door 328 for receiving a bundle of wood from anexternal environment and a reactor exit door 329 for discharging thebundle of wood from chemical modification reactor 322 after chemicalmodification. In addition, heater 332 can comprise a heater entrancedoor 328 for receiving the bundle of chemically-modified, chemical-wetwood discharged from chemical modification reactor 322. According to oneembodiment, heater 332 can also include a heater exit door 339 separatefrom heater entrance door 338 for discharging a bundle of wood fromheater 332. In one embodiment, respective reactor and heater entrancedoors 328, 338 and reactor or heater exit doors 329, 339, when present,can be positioned on a generally opposite end of reactor 322 or heater332 such that the respective central axes of elongation of reactor 322and heater 332, represented as axes 370 a,b in FIG. 4 b, can extendthrough respective entrance 328, 338 and exit 329, 339 doors. In oneembodiment, reactor 322 and heater 332 are axially aligned with oneanother such that the central axes of elongation 370 a,b in FIG. 4 b,are substantially aligned with one another, while, in other oneembodiment, axes 370 a,b can be parallel to each other. As used herein,the term “substantially aligned” refers to two or more vesselsconfigured such that the maximum acute angle formed between theintersection of their respective central axes of elongation is not morethan about 20°. In some embodiments, the maximum acute angle between theintersection of the two axes of elongation of substantially alignedvessels can be not more than about 10°, not more than about 5°, not morethan about 2°, or not more than about 1°. In some embodiments, reactor322 and heater 332 can be arranged in a side-by-side configuration (notshown).

According to one embodiment shown in FIG. 4 a, vapor containment room360 can be sealingly coupled to reactor 322 and heater 332 such that theexternal environment is substantially isolated from transfer region 361during transport of the bundle of wood from reactor 322 to heater 332.As used herein, the term “sealingly coupled” refers to two or moreobjects attached, fastened, or otherwise associated such that leakage offluid is substantially reduced or nearly prevented from the junction ofsuch objects. In one embodiment, reactor entrance door 328 and/or heaterexit door 339, when present, can open to the external environment, whilereactor exit door 329 and/or heater entrance door 338 can open to theinterior of vapor containment room 360, thereby isolating the externalenvironment from vapor or gases from chemical reactor 322, heater 332,and/or the bundle of chemical-wet wood during transport between reactor322 and heater 332 via transfer region 361.

Vapor containment room 360 can be configured in any manner suitablemanner. In one embodiment depicted in FIGS. 4 a and 4 b, vaporcontainment room 360 comprises four generally upright walls 342 a-dcoupled to a ceiling structure 344 and a floor (not shown). Althoughillustrated in FIGS. 4 a and 4 b as being generally attached to ceilingstructure 344, a vapor outlet conduit 349 for removing vapors and gasesfrom the interior of vapor containment room 360 could alternatively beattached to one of walls 342 a-d or to the floor. Additional detailsregarding the removal of vapors and gases from vapor containment room360 will be described in more detail shortly.

In one embodiment of the present invention, at least one of walls 342a-d can comprise at least one blast panel or blast wall 343 forcontrolling the direction of a pressure release in the event of anexplosion or rapid pressurization within vapor containment room 360. Inone embodiment, blast panel 343 can be attached to the ceiling 344and/or floor (not shown) of vapor containment room 360. Blast panel orwall 343 can be hinged, tethered, or otherwise fastened to anotherstructure of vapor containment room 360 in order to prevent or reducethe likelihood that blast panel or wall 343 will be freely projected atan undesirable velocity away from vapor containment room 360 by anexplosion. Blast panel or wall 343 can have a substantially solidsurface, as shown in FIG. 4 b, or can comprise a plurality of slats orslots (not shown). Typically, the sections of walls 342 a-d that are notblast panels/walls 343 are construction of a high-strength materialssuch as, for example, precast concrete panels, concrete blocks, or steelpanels. Although illustrated herein as having four walls, it should beunderstood that vapor containment rooms having various other shapes canalso be employed.

As depicted in FIG. 4 c, vapor containment room 360 can be equipped withone or more vents 370 a,b for selectively permitting fluid flow from theexternal environment into the interior of vapor containment room 360. Inone embodiment, vents 370 a,b are one-way vents that permit fluid flowfrom the external environment into vapor containment room 360, asindicated by arrows 380 a,b in FIG. 4 c, but reduce, inhibit, orsubstantially prevent fluid flow from the interior of vapor containmentroom 360 out into the external environment. Examples of external fluidsthat can flow into vapor containment room 360 via vents 370 a,b includeambient air or one or more inert gases such as nitrogen.

In one embodiment, vents 370 a,b, can be configured to maintain apredetermined pressure difference between the interior of vaporcontainment room 360 and the external environment. By maintaining apredetermined pressure difference between the interior of vaporcontainment room 360 and the external environment, vents 370 a,b cancontrol the rate at which a fluid from the external environment is drawninto vapor containment room 360. To maintain a relatively constantpressure difference between the interior of vapor containment room 360and the external environment, vents 370 a,b can be equipped with acontrol mechanism (e.g., an electronic actuator, a hydraulic actuator, apneumatic actuator, or a mechanical spring) for varying the degree ofopenness of vents 370 a,b based on the pressure difference across vents370 a,b. When the pressure difference between the external environmentand the interior of the vapor containment room 360 is too high, vents370 a,b open wider, and, analogously, when the pressure difference istoo low, vents 370 a,b move towards a closed position. In oneembodiment, vents 370 a,b, can be spring loaded and biased towards theclosed position, so that when the pressure difference between the vaporcontainment room 360 and the external environment is below a thresholdvalue, vents 370 a,b are closed, but when the pressure in vaporcontainment room 360 is lower than the pressure of the externalenvironment by an amount exceeding the threshold pressure differencevalue, vents 370 a,b open to allow an external fluid to be drawn intovapor containment room 360.

Further, when vents 370 a,b are spring loaded, the vents help maintain asubstantially constant pressure difference between the interior of vaporcontainment room 360 and the external environment by automaticallyopening wider when the pressure difference is high and automaticallymoving towards the closed position when the pressure difference is low.In one embodiment, vapor containment room 360 is maintained at asub-atmospheric pressure during transport and can be maintained at avacuum of at least about 0.05 inches of water, at least about 0.1 inchesof water, or at least about 0.15 inches of water and/or no more thanabout 10 inches of water, no more than about 1 inch of water, or no morethan about 0.5 inches of water. In one embodiment, vents 370 a,b, areconfigured to permit fluid from the external environment (e.g., ambientair) to be drawn into vapor containment room 360 at a rate that causesat least about 2, at least about 4, or at least about 5 exchanges perhour to be drawn out of vapor containment room 360, where one exchangeis equal to one volume of vapor containment room 360. As used herein,the term “exchanges per hour” refers to the total number of times perhour that the total volume of fluid in the system is replaced,calculated by dividing the volumetric flow rate of vapor removed fromthe system by the total system volume.

In one embodiment, the size of vapor containment room 360 can be suchthat the reactor and heater 322, 332 (e.g., positioning the internalvolumes of the reactor and heater) are spaced apart from each other by adistance that is at least about 2 feet, at least about 4 feet, or atleast about 6 feet and/or no more than about 50 feet, no more than about30 feet, or no more than about 20 feet. In one embodiment, the length ofthe vapor containment room can be the same as, or substantially the sameas, the distance between reactor 322 and heater 332. According to oneembodiment, the ratio of the length of vapor containment room 360 to thetotal length of reactor 322 and/or the total length of heater 332 can beat least about 0.1:1, at least about 0.2:1, or at least about 0.3:1and/or no more than about 1:1, no more than about 0.6:1, or no more thanabout 0.5:1. When the space between reactor 322 and heater 332 isminimized, reactor exit door 329 and heater entrance door 338 may becapable of contacting one another during opening. In such an embodiment,reactor exit door 329 and heater entrance door 338 can be configured tonest/overlap with one another (but not contact one another) when theyare both fully opened.

FIG. 4 d is a side view of a wood treatment facility 416 comprising areactor 322, a heater 332, and a vapor containment room 360 disposedtherebetween. FIG. 4 d additionally depicts an embodiment that employs aproduct vapor removal system or structure 400 located near exit door 339of heater 332. Product vapor removal system 400 can be configured totransport vapors out of and away from the area near exit door 339 ofheater 332 (e.g. the recovery room). This configuration cansubstantially reduce and, in some embodiments can nearly prevent escapeof vapors from the chemically-treated bundle of wood exiting heater 332and/or from vapors exiting reactor 322 and/or heater 332 to the externalenvironment. As shown in FIG. 4 d, both vapor containment room 360 andproduct vapor removal system 400 can be connected or otherwise operablycoupled to a common ventilation system 402. Ventilation system 402 isused to draw vapors and gases out of vapor containment room 360 and/orthrough product vapor removal system 400. Although FIG. 4 d illustratesone common ventilation system 402 being used for both vapor containmentroom 360 and product vapor removal system 400, it is possible to useindividual ventilation systems for each containment/ventilation area ofthe wood treatment facility.

In the embodiment depicted in FIG. 4 d, product vapor removal system 400comprises a ventilation hood 404 and a ventilation room 406 disposedbetween ventilation hood 404 and heater 332. Ventilation hood 404 andventilation room 406 can be connected to ventilation system 402, whichdraws vapor out of ventilation hood 404 and/or ventilation room 406.Ventilation room 406 can be configured to receive a bundle ofchemically-modified wood through heater exit door 339, which opens intoventilation room 406.

Ventilation room 406 can be equipped with a ventilation room exit 408through which the chemically-modified wood passes to a cooling locationbelow ventilation hood 404. In one embodiment, ventilation room exit 408can be equipped with a door 409 that, when closed, substantiallyisolates the external environment from the interior of ventilation room406. When ventilation room is equipped with such a door, ventilationroom may also be equipped with vents (not shown) similar to vents 370a,b of vapor containment room 360, described previously with referenceto FIG. 4 c. However, in another embodiment, ventilation room exit 408is configured to constantly permit passage of fluid from the externalenvironment into the interior of ventilation room 406. In such anembodiment, ventilation room exit 408 can be entirely open so as topermit free flow of fluid therethrough. Alternatively, ventilation roomexit 408 can be partially covered with a flexible material (e.g., ahanging VISQUEEN sheet or strips of VISQUEEN) that permits passage ofthe bundle of chemically-treated wood therethrough, but that at leastpartially inhibits free flow of fluid therethrough. In one embodiment ofthe present invention, ventilation room 406 can be entirely eliminatedand ventilation hood 404 can be positioned adjacent exit door 339 ofheater 332.

As shown in FIG. 4 d, ventilation system 402 can include one or morevacuum generators 410, a treatment device 412, a flow diverter 414, anda plurality of vapor outlet conduits 349 a-c. Vacuum generator 410 canbe operable to draw vapor out of vapor containment room 360, ventilationhood 404, and/or ventilation room 406 via outlet conduits 349 a,b,c,respectively. Treatment device 412 can be operable to remove or tochange the composition of at least a portion of one or more componentsfrom the vapors drawn out of vapor containment room 360, ventilationhood 404, and/or ventilation room 406 via vacuum generator 410. Examplesof suitable treatment devices can include, but are not limited to,scrubbers, thermal oxidizers, catalytic oxidizers or other catalyticprocesses, and/or precipitators.

According to one embodiment, flow diverter 414 can be operable adjustthe total ventilation capacity of vacuum generator 410 by, for example,directing the vapor flow amongst vapor outlet conduits 349 a,b,c therebydistributing the total ventilation capacity of ventilation system 402between vapor containment room 360, and product vapor removal structure(e.g., ventilation hood 404, and/or ventilation room 406). As usedherein, the term “total ventilation capacity” refers to the maximumvolume of vapors removable from the system via a vacuum generator orother source, expressed as a time-based rate. Distribution of the totalventilation capacity amongst vapor containment room 360, ventilationhood 404, and/or ventilation room 406 may be advantageous, for example,to accommodate the various steps of a chemical modification treatment.In one embodiment, flow diverter 414 can be operable to evenlydistribute the total ventilation capacity, represented generically as“X”, such that ⅓X is provided to vapor containment room 360, ⅓X isprovided to ventilation hood 404, and ⅓X is provided to ventilation room406. In another exemplary embodiment, flow diverter 414 can allocatemore ventilation capacity to one of the three areas, such as, forexample vapor containment room 360, so that ⅔X is provided to vaporcontainment room 360, ⅙X is provided to ventilation hood 404, and ⅙X isprovided to ventilation room 406.

One embodiment of the operation of wood treatment facility 416 will nowbe described in detail, with respect to FIG. 4 d. A first bundle ofwood, represented herein by the letter “C,” can be loaded into chemicalmodification reactor 322 via reactor entrance door 328 and chemicallytreated. Simultaneously, a second bundle of wood, represented here bythe letter “B,” can be introduced into heater 332 via heater entrancedoor 338 and heated and/or dried. While bundles C and B are beingchemically-modified and heated/dried in chemical modification reactor322 and heater 332, respectively, a third bundle of wood, representedherein with the letter “A”, can be removed from ventilation room 406 andpositioned under ventilation hood 404, as generally shown in FIG. 4 d.

Once bundle A has been sufficiently dried, it can be removed fromventilation hood 404 and transported to a storage area (not shown).Then, the allocation of the total ventilation capacity of ventilationsystem 402 can be adjusted using flow diverter 414 such that amount ofventilation capacity allocated to vapor containment room 360 isincreased, while the amount of ventilation capacity allocated toventilation hood 404 is decreased. Next, after completion of the heatingof bundle “B”, heater entrance and exit doors 338, 339 can be openedconsecutively and any residual vapor or gas present in the interior ofheater 332 can be removed and passed through vapor containment room 360before entering ventilation system 402. In one embodiment, thisevacuation of heater 332 can also comprise drawing an external fluid(e.g., ambient air or other inert gas) into the system throughventilation hood 404 and ventilation room 406, when present. Theexternal fluid can then enter heater 332 via heater exit door 339 andpass through the interior of heater 332, before exiting heater 332 viaheater entrance door 338 and passing into vapor containment room 360.Once in vapor containment room 360, the external fluid, along with anyresidual vapor or gas removed from the interior of heater 332, can bewithdrawn from vapor containment room 360 by way of ventilation system402 at a rate of at least about 2 exchanges per hour, at least about 4exchanges per hour, or at least about 6 exchanges per hour. For example,if the ventilation system had a total volume of 100 cubic meters and therate of vapor removal was 200 cubic meters per hour, the exchanges perhour would be (200 cubic meters per hour)/(100 cubic meters) or 2exchanges per hour.

Once the external fluid and residual vapor/gas has been removed fromvapor containment room 360, bundle B can be removed from heater 332 viaheater exit door 339, passed through ventilation room 406 (if present),and positioned under ventilation hood 404 to cool and/or further drybundle B, as discussed in detail previously. Heater exit door 339 canthen be closed before reactor exit door 329 and reactor entrance door328 are sequentially opened. Thereafter, ventilation system 402 can beused to evacuate residual vapor or gas from the interior of chemicalmodification reactor 322. In one embodiment, an external fluid (e.g.,ambient air or other inert gas) can be drawn into reactor 322 viareactor entrance door 328 and pass through the interior of reactor 322before exiting into vapor containment room 360 via reactor exit door329. As described above, the external fluid and any residual vapors orgases can then be withdrawn from vapor containment room 360 via vaporoutlet conduit 349 a at a rate of at least about 2 exchanges per hour,at least about 4 exchanges per hour, or at least about 6 exchanges perhour.

Thereafter, bundle C can be removed from chemical modification reactor322 via reactor exit door 329 and passed through vapor containment room360 along a transport path 399. In one embodiment, product ventilationsystem 402 can be used to draw gases and vapors from vapor containmentroom 360 during the transportation of the bundle between reactor 322 andheater 332. Chemically-wet bundle C can then be introduced into theinterior of heater 332 via heater entrance door 338, prior to initiatingheating of bundle C. Next, a fourth bundle (not shown) can be loadedinto the interior of chemical modification reactor 322 before closing,in sequence, reactor entrance door 328, reactor exit door 329, andheater entrance door 338. The allocation of total ventilation capacityto vapor containment room 360 can be decreased, while increasing theallocation to ventilation hood 404, to thereby cool and/or further drybundle B. A fifth bundle (not shown) can be assembled, either in aloading area (not shown) or near reactor entrance door 328 beforerepeating the above-referenced steps to process a new sequence of woodbundles.

It should be understood that, in the above-described operationalsequence, some steps can preferably be carried out in the orderdescribed, while some steps can be carried out simultaneously and/or theorder of some steps can be switched. The above sequence of steps isincluded simply to describe one exemplary method of operating woodtreatment system 416.

Microwave Heating Systems

According to one embodiment, one or more of the heating systemsdescribed above can comprise microwave heating systems that utilizemicrowave energy to heat one or more objects or items. In addition toone embodiment of the wood treatment facilities described above,microwave heating systems configured according to one embodiment of thepresent invention have wide applicability to a variety of otherprocesses. It should be understood that, while predominantly describedherein with respect to processes for heating “wood” or a “bundle ofwood,” the processes and systems described herein are equally applicableto applications wherein one or more articles, objects, or loads areheated. Examples of other types of application that can utilizemicrowave heating systems as described herein can include, but are notlimited to, high temperature vacuum ceramic and metal sintering,melting, brazing, and heat treating of various materials. In oneembodiment, the microwave heating system can include a vacuum system(e.g., a microwave vacuum heater) and can be utilized for vacuum dryingof materials such as minerals and semiconductors, vacuum drying offoodstuffs such as fruits and vegetables, vacuum drying of ceramic andfibrous molds, as well as vacuum drying of chemical solutions.

Turning now to FIG. 5, a microwave heating system 420 configuredaccording to one embodiment of the present invention is illustrated ascomprising at least one microwave generator 422, a microwave heater 430,a microwave distribution system 440, and an optional vacuum system 450.Microwave energy produced by microwave generator 422 can be directed tomicrowave heater 430 via one or more components of microwavedistribution system 440. Additional details regarding components andoperation of microwave distribution system 440 will be discussed indetail shortly. When present, vacuum system 450 can be operable toreduce the pressure in microwave heater 430 to no more than about 550torr, no more than about 450 torr, no more than about 350 torr, no morethan about 250 torr, no more than about 200 torr, no more than about 150torr, no more than about 100 torr, or no more than about 75 torr. In oneembodiment, the vacuum system can be operable to reduce the pressure inmicrowave heater 430 to no more than about 10 millitorr (10⁻³ torr), nomore than about 5 millitorr, no more than about 2 millitorr, no morethan about 1 millitorr, no more than about 0.5 millitorr, or no morethan about 0.1 millitorr. Each of the components of microwave heatingsystem 420 will now be discussed in detail below.

Microwave generator 422 can be any device capable of producing orgenerating microwave energy. As used herein, the term “microwave energy”refers to electromagnetic energy having a frequency between 300 MHz and30 GHz. In one embodiment, various configurations of microwave heatingsystem 420 can utilize microwave energy having a frequency of about 915MHz or a frequency of about 2.45 GHz, both of which have been generallydesignated as industrial microwave frequencies. Examples of suitabletypes of microwave generators can include, but are not limited to,magnetrons, klystrons, traveling wave tubes, and gyrotrons. In variousembodiments, one or more microwave generators 422 can be capable ofdelivering (e.g., have a maximum output of) at least about 5 kW, atleast about 30 kW, at least about 50 kW, at least about 60 kW, at leastabout 65 kW, at least about 75 kW, at least about 100 kW, at least about150 kW, at least about 200 kW, at least about 250 kW, at least about 350kW, at least about 400 kW, at least about 500 kW, at least about 600 kW,at least about 750 kW, or at least about 1,000 kW and/or not more thanabout 2,500 kW, not more than about 1,500 kW, or not more than about1,000 kW. Although illustrated as comprising one microwave generator422, microwave heating system 420 can comprise two or more microwavegenerators configured to operate in a similar manner.

Microwave heater 430 can be any device capable of receiving and heatingone or more articles, including, for example, bundles of wood or lumber,using microwave energy. In one embodiment, at least about 75 percent, atleast about 85 percent, at least about 95 percent, or substantially allof the heat or energy provided by microwave heater 430 can be providedby microwave energy. Microwave heater 430 can also be used as amicrowave dryer, which can be further operable to dry one or more itemsdisposed therein using microwave energy as described herein.

Turning now to FIG. 6, one embodiment of a microwave heater 530 isillustrated as comprising a vessel body 532 and a door 534 forselectively permitting and blocking the access to or passage of one ormore objects (not shown) into and out of the interior 536 of microwaveheater 530. In one embodiment, vessel body 532 of microwave heater 530can be elongated along a central axis of elongation 535, which can beoriented in a substantially horizontal direction, as illustrated in FIG.6. Vessel body 532 can have a cross-section of any suitable shape orsize. In one embodiment, the cross-section of vessel 532 can besubstantially circular or round, while, in another embodiment, thecross-section can be elliptical. According to one embodiment, the sizeand/or shape of the cross-section of vessel body 532 can change alongthe direction of elongation, while, in another embodiment, the shapeand/or size of its cross-section can remain substantially the same. Inthe embodiment depicted in FIG. 6, vessel body 532 of microwave heater530 comprises a horizontally elongated, cylindrical vessel body having acircular cross-section.

Microwave heater 530 can have an overall maximum internal dimension orlength, L, and a maximum inner diameter, D, as shown in FIG. 6. In oneembodiment, L can be at least about 8 feet, at least about 10 feet, atleast about 16 feet, at least about 20 feet, at least about 30 feet, atleast about 50 feet, at least about 75 feet, at least about 100 feetand/or no more than about 500 feet, no more than about 350 feet, no morethan about 250 feet. In another embodiment, D can be at least about 3feet, at least about 5 feet, at least about 10 feet, at least about 12feet, at least about 18 feet, at least about 20 feet, at least about 25feet, or at least about 30 feet and/or no more than about 25 feet, nomore than about 20 feet, or no more than about 15 feet. In oneembodiment, the ratio (L:D) of the length of microwave heater 530 to itsinner diameter (L:D) can be at least about 1:1, at least about 2:1, atleast about 3:1, at least about 4:1, at least about 6:1, at least about8:1, at least about 10:1 and/or no more than about 50:1, no more thanabout 40:1, or no more than about 25:1.

Microwave heater 530 can be constructed out of any suitable material. Inone embodiment, microwave heater 530 can comprise at least oneelectrically conductive and/or highly reflective material. Examples ofsuitable materials can include, but are not limited to, selected carbonsteels, stainless steels, nickel alloys, aluminum alloys, and copperalloys. Microwave heater 530 can be almost completely constructed out ofa single material, or multiple materials can be used to constructvarious portions of microwave heater 530. For example, in oneembodiment, microwave heater 530 can be constructed of a first materialand can then be coated or layered with a second material on at least aportion of its interior and/or exterior surface. In one embodiment, thecoating or layer can comprise one or more of the metals or alloys listedabove, while, in another embodiment, the coating or layer can compriseglass, polymer, or other dielectric material.

Microwave heater 530 can define one or more spaces suitable forreceiving a load. For example, in one embodiment, microwave heater 530can define a bundle-receiving space configured to receive and hold oneor more bundles of wood (not shown in FIG. 6). The load (e.g., wood) canbe positioned within interior 536 of microwave heater 530 in a static ordynamic manner. For example, in one embodiment wherein the load isstatically positioned in microwave heater 530, the load can berelatively motionless during heating and may be held in place usingstatic positioning devices (not shown) such as, for example, a shelf, aplatform, a parked cart, a stopped belt, or the like. In anotherembodiment wherein the load is dynamically positioned within microwaveheater 530, the load can be in motion during at least a portion ofheating using one or more dynamic positioning devices (not shown) duringheating. Examples of dynamic positioning devices can include, but arenot limited to, continuous moving belts, rollers, horizontally and/orvertically oscillating platforms, and rotating platforms. In oneembodiment, one or more dynamic positioning devices may be used in agenerally continuous process, while one or more static positioningdevices may be employed in a batch or semi-batch process.

According to one embodiment of the present invention, microwave heater530 can also comprise one or more sealing mechanisms to reduce, inhibit,minimize, or substantially prevent the leakage of fluids and/ormicrowave energy into or out of the vessel interior 536 duringtreatment. As illustrated in FIG. 6, vessel body 532 and door 534 caneach present respective body-side and door-side sealing surfaces 531,533. In one embodiment, body-side and door-side sealing surfaces 531,533 can directly or indirectly form a fluid seal between door 534 andvessel body 532 when door 534 is closed. A direct seal can be formedwhen at least a portion of body-side and door-side sealing surfaces 531,533 make direct physical contact with one another. An indirect seal canbe formed between door 534 and vessel body 532 when one or moreresilient sealing members for fluidly isolating the interior ofmicrowave heater 530 from an external environment (not shown in FIG. 6)are at least partially compressed against door-side and/or body-sidesealing surfaces 533, 531 when door 534 is closed. Examples of resilientsealing members can include, but are not limited to, o-rings, spiralwound gaskets, sheet gaskets, and the like. According to one embodiment,the direct or indirect seal formed between vessel body 532 and door 534can be such that microwave heater 530 can have a fluid leak rate of nomore than about 10⁻² torr liters/sec, no more than about 10⁻⁴ torrliters/sec, or no more than about 10⁻⁸ torr liters/sec at or near thejunction of body 532 and door 534, when subjected to a helium leak testconducted according to procedure B1 entitled “Spraying Testing”described in the document entitled “Helium Leak Detection Techniques”published by Alcatel Vacuum Technology using a Varian Model No. 938-41detector. In one embodiment, fluid seal can be particularly useful whenthe environment inside microwave heater 530 comprises a sub-atmosphericand otherwise challenging process environment.

Microwave heaters configured according to one embodiment of the presentinvention can also comprise a microwave choke for inhibiting orsubstantially preventing microwave energy leakage between door 534 andvessel body 532 of microwave heater 530 when door 534 is closed (e.g.,at or near the junction of door 534 and vessel body 532). As usedherein, the term “choke” refers to any device or component of amicrowave vessel operable to reduce the amount of energy leaking from orescaping the vessel during the application of microwave energy. In oneembodiment, the choke can be any device operable to reduce the amount ofmicrowave leakage from the vessel by at least about 25 percent, at leastabout 50 percent, at least about 75 percent, or at least about 90percent as compared to when a choke is not employed. In one embodimentof the present invention, the microwave choke can be operable to allowno more than about 50 milliwatts per square centimeter (mW/cm²), no morethan about 25 mW/cm², no more than about 10 mW/cm², no more than about 5mW/cm², or no more than about 2 mW/cm² of microwave energy to leak outof the heater through the choke when measured 5 cm from the vessel witha Narda Microline Model 8300 broad band isotropic radiation monitor (300MHz to 18 GHz).

Further, in contrast to conventional microwave chokes, which often failwhen subjected to sub-atmospheric pressures, microwave chokes configuredaccording to one embodiment of the present invention can be operable tosubstantially inhibit microwave energy leakage, even under deep vacuumconditions. For example, in one embodiment, a microwave choke asdescribed herein can inhibit microwave energy leakage from the heater tothe extent described above when the pressure in the microwave heater isno more than about 550 torr, no more than about 450 torr, no more thanabout 350 torr, no more than about 250 torr, no more than about 200torr, no more than about 100 torr, or no more than about 75 torr. In oneembodiment, a microwave choke as described herein can inhibit microwaveenergy leakage from the heater to the extent as described above when thepressure in the microwave heater is no more than about 10 millitorr(10⁻³ torr), no more than about 5 millitorr, no more than about 2millitorr, no more than about 1 millitorr, no more than about 0.5millitorr, or no more than about 0.1 millitorr. Further, a microwavechoke according to one embodiment of the present invention can maintainits level of leakage prevention on large-scale units, such as, forexample, microwave heaters having a microwave energy input rate of atleast about 5 kW, at least about 30 kW, at least about 50 kW, at leastabout 60 kW, at least about 65 kW, at least about 75 kW, at least about100 kW, at least about 150 kW, at least about 200 kW, at least about 250kW, at least about 350 kW, at least about 400 kW, at least about 500 kW,at least about 600 kW, at least about 750 kW, or at least about 1,000 kWand/or not more than about 2,500 kW, not more than about 1,500 kW, ornot more than about 1,000 kW.

In one embodiment, substantially no arcing can occur near the choke 650while microwave energy is introduced into the vessel (e.g., during theheating step), even at the levels of microwave energy and vacuumpressure described above. As used herein, the term “arcing”, refers toundesired, uncontrolled electrical discharge, at least partially causedby ionization of a surrounding fluid. Arcing, which can damage equipmentand materials and poses a substantial fire or explosion hazard, has alower threshold at lower pressures, especially sub-atmospheric (e.g.,vacuum) pressures. Typically, conventional systems limit rate of energyinput in order to minimize or avoid arcing. In contrast to conventionalsystems, however, microwave heaters configured according to embodimentsof the present invention can be operable to receive microwave energy ata rate of at least about 5 kW, at least about 30 kW, at least about 50kW, at least about 60 kW, at least about 65 kW, at least about 75 kW, atleast about 100 kW, at least about 150 kW, at least about 200 kW, atleast about 250 kW, at least about 350 kW, at least about 400 kW, atleast about 500 kW, at least about 600 kW, at least about 750 kW, or atleast about 1,000 kW and/or not more than about 2,500 kW, not more thanabout 1,500 kW, or not more than about 1,000 kW can be introduced into amicrowave heater (optionally referred to as a vacuum microwave heater ora vacuum microwave dryer) when the pressure is no more than about 550torr, no more than about 450 torr, no more than about 350 torr, no morethan about 250 torr, no more than about 200 torr, no more than about 100torr, no more than about 75 torr, no more than about 10 millitorr (10⁻³torr), no more than about 5 millitorr, no more than about 2 millitorr,no more than about 1 millitorr, no more than about 0.5 millitorr, or nomore than about 0.1 millitorr and/or at least about 50 torr or at leastabout 75 torr with substantially no arcing at or near the choke.

Referring now to FIG. 7 a, a cross-sectional segment of one embodimentof a microwave choke 650 for substantially inhibiting microwave energyleakage between a door 634 and a vessel body 632 of a microwave heaterwhen door 634 is closed is provided. As shown in FIG. 7 a, at least aportion of microwave choke 650 is cooperatively defined or formedbetween door 634 and vessel body 632 when door 634 is closed andrespective door-side 633 and body-side 631 sealing surfaces are indirect or indirect contact with one another. In one embodiment, anoptional fluid sealing member 660 can also be present to inhibit,minimize, or substantially prevent leakage of fluid into or out of themicrowave heater, as discussed previously. Fluid sealing member 660,when present, can be coupled to vessel body 632 or, as shown in FIG. 7a, to door 634.

According to one embodiment shown in FIG. 7 a, microwave choke 650defines a first radially-extending choke cavity 652, a second-radiallyextending choke cavity 654, and a radially-extending choke guidewall 656disposed at least partly between first and second choke cavities 652,654 when the door 634 of the microwave heater is closed. In oneembodiment illustrated in FIG. 7 a, first choke cavity 652 is definedbetween vessel body 632 and choke guidewall 656 when door 634 is closed,while second choke cavity 654 is at least partially disposed betweendoor 634 and choke guidewall 656, such that choke guidewall 656 issubstantially coupled to door 634. First choke cavity 652 can be open tothe interior of the microwave heater and can be radially positionedbetween the interior of the microwave heater and the fluid seal createdby sealing member 660, when present. In another embodiment of thepresent invention (not shown in FIG. 7 a), second choke cavity 654 canbe at least partially defined by vessel body 632, such that second chokecavity 654 can be positioned between vessel body 632 and choke guidewall656 when door 634 is closed, such that choke guidewall 656 issubstantially coupled to vessel body 632.

In one embodiment, at least a portion of second choke cavity 654 canextend alongside at least a portion of first choke cavity 652 when door634 is closed. In one embodiment, at least about 40 percent, at leastabout 60 percent, at least about 80 percent, or at least about 90percent of the total length of second choke cavity 654 can extendalongside first choke cavity 654 when door 634 is closed. The totallength of first and/or second choke cavities 652, 654, designated withthe letter “L” in FIG. 7 a, can be at least about 1/16 times, at leastabout ⅛ times, at least about ¼ times and/or no more than about 1 times,no more than about ¾ times, or no more than about ½ times the length ofthe predominant wavelength of the microwave energy in the interior ofthe microwave heater. The length, L, of first and/or second chokecavities 652, 654 can be at least about 1 inch, at least about 1.5inches, at least about 2 inches, or at least about 2.5 inches and/or nomore than about 8 inches, no more than about 6 inches, or no more thanabout 5 inches.

As illustrated in FIG. 7 b, a relative extension angle, φ, can bedefined between the direction of extension of first choke cavity 652,designated by line 690, and the direction of extension of second chokecavity 654, designated by line 692. In various embodiments, the relativeextension angle, φ, can be no more than about 60°, no more than about45°, no more than about 30°, or no more than about 15°. In someembodiments, the direction of extension of second choke cavity 654 canbe substantially parallel to the direction of extension of first chokecavity 652, as depicted in FIG. 7 a.

Referring now to FIG. 7 c, a partial isometric cross-sectional portionof a microwave choke is provided. As shown in FIG. 7 c, choke guidewall656 can be integrally formed into door 634. According to one embodiment,guidewall 656 can comprise a plurality of spaced open-ended gaps 670disposed circumferentially along guidewall 656. In one embodiment, thespacing between the centerline of each of the gaps can be at least about0.5 inches, at least about 1 inch, at least about 2 inches, or at leastabout 2.5 inches and/or no more than about 8 inches, no more than about6 inches, or no more than about 5 inches.

According to another embodiment of the present invention, at least aportion of choke 650 can comprise a removable portion 651 removablycoupled to vessel body 632 or door 634. In one embodiment, removableportion 651 can be removably coupled to door 634. As used herein, theterm “removably coupled” means attached in a manner such that a portionof the choke can be removed without substantial damage to or destructionof the vessel body, the choke, and/or the door. In one embodiment,removable choke portion 651 can comprise at least a portion or all ofguidewall 656. FIG. 7 d illustrates a microwave choke having at leastone removable portion 651. In one embodiment depicted in FIG. 7 d,guidewall 656 can be coupled to removable choke portion 651. Removablechoke portion 651 can comprise a plurality of removable choke segments653 a-e that are each removably coupled to door 634 or vessel body 632(embodiment not shown). In one embodiment, removable choke portion 651can comprise at least 2, at least 3, at least 4, at least 6, at least 8and/or no more than 16, no more than 12, no more than 10, or no morethan 8 removable choke segments 653. According to one embodiment whereinremovable choke portion 651 has a generally ring-shaped diameter,individually removable choke segments 653 a-e can have a generallyarcuate shape, as shown in FIG. 7 d.

Removable choke portion 651 can be fastened to door 634 or vessel body632 according to any known method including, for example, bolts, screws,or any other type of suitable removable fastening device. In oneembodiment, removable choke portion 651 can be magnetically fastened todoor 634 or vessel body 632. Depending, in part, on the desired methodof fastening, removable choke portion 651 can have a variety ofcross-sectional shapes. For example, as illustrated in FIGS. 7 e-h,removable choke portion 651 can define a cross-section which isgenerally G-shaped (as shown in FIG. 7 e), generally J-shaped orU-shaped (as shown in FIG. 7 f), generally L-shaped (as shown in FIG. 7g), or generally I-shaped (as shown in FIG. 7 h).

In operation, removable choke portion 651 can be attached, removed,and/or subsequently replaced without removing portions of orsubstantially re-machining vessel body 632 and/or door 634 in order toresume normal operation of the microwave heater. For example, in oneembodiment, a plurality of individually removable choke segments 653 a-ecan be separately and individually attached to door 634 and/or vesselbody 632. Subsequently, when one or more portions of the microwave chokebecome damaged or otherwise require replacement, one or moreindividually removable choke segments 653 and/or the entire removablechoke portion 651 can be separately and individually detached or removedfrom vessel body 632 or door 634 and replaced with one or more new(e.g., replacement) removable choke segments 653 and/or a new removablechoke portion 651. In one embodiment, the number of removable chokesegment or segments 653 a, b, c, d, and/or e detached from and thenreattached to (e.g., removed from and replaced onto) vessel body 632 ordoor 634 can be not more than or no more than the total number of chokesegments 653 a-e of removable portion 651.

Microwave heater 530, generically represented in FIG. 6, can beclassified as a single mode cavity, a multi-mode cavity, or aquasi-optical cavity depending on how the microwave energy thereinbehaves. As used herein, the term “single mode cavity” refers to acavity designed and operated to maintain the microwave energy therein asingle, specific mode pattern. Oftentimes, the design and properties ofa single mode cavity can limit the size of the vessel and/or how a loadcan be positioned within the chamber. As a result, in one embodiment,microwave heater 530 can comprise a multimode or a quasi-optical modecavity. As used herein, the term “multimode cavity” refers to a cavityor chamber wherein the microwave energy is excited into a plurality ofstanding wave patterns in a semi-random or undirected manner. As usedherein, the term “quasi-optical mode cavity” refers to a cavity orchamber wherein most, but not all, of the energy is directed toward aparticular area in a controlled manner. In one embodiment, a multimodecavity has a higher energy density near the center of the vessel than aquasi-optical cavity, while quasi-optical cavities can leverage thequasi-optical properties of microwave energy to more closely control anddirect the emission of energy into the cavity interior.

Turning back to microwave heating system 420 illustrated in FIG. 5,microwave distribution system 440 is operable to transmit or direct atleast a portion of the microwave energy produced by microwave generator422 into microwave heater 430, as discussed briefly above. As shownschematically in FIG. 5, microwave distribution system 440 can includeat least one waveguide 442 operably coupled to one or more microwavelaunchers, illustrated as launchers 444 a-c. Optionally, microwavedistribution system 440 can comprise one or more microwave modeconverters 446 for changing the mode of the microwave energy passingtherethrough and/or one or more microwave switches (not shown) forselectively routing microwave energy to one or more of microwavelaunchers 444 a-c. Additional details regarding specific components andvarious embodiments of microwave distributions system 440 will now bediscussed in detail below.

Waveguides 442 can be operable to transport microwave energy frommicrowave generator 422 to one or more of microwave launchers 444 a-c.As used herein, the term “waveguide” refers to any device or materialcapable of directing electromagnetic energy from one location toanother. Examples of suitable waveguides can include, but are notlimited to, co-axial cables, clad fibers, dielectric-filled waveguides,or any other type of transmission line. In one embodiment, waveguides442 can comprise one or more dielectric-filled waveguide segments fortransporting microwave energy from microwave generator 422 to one ormore of launchers 444 a-c.

Waveguides 442 can be designed and constructed to propagate microwaveenergy in a specific predominant mode. As used herein, the term “mode”refers to a generally fixed cross-sectional field pattern of microwaveenergy. In one embodiment of the present invention, waveguides 442 canbe configured to propagate microwave energy in a TE_(xy) mode, wherein xis an integer in the range of from 1 to 5 and y is 0. In anotherembodiment of the present invention, waveguides 442 can be configured topropagate microwave energy in a TM_(ab) mode, wherein a is 0 and b is aninteger in the range of from 1 to 5. It should be understood that, asused herein, the above-defined ranges of a, b, x, and y values as usedto describe a mode of microwave propagation are applicable throughoutthis description. Further, in some embodiments, when two or morecomponents of a system are described as being “TM_(ab)” or “TE_(xy)”components, the values for a, b, x, and/or y can be the same ordifferent for each component. In one embodiment, the values for a, b, x,and/or y are same for each component of a given system.

The shape and dimensions of waveguides 442 can depend, at least in part,on the desired mode of the microwave energy to be passed therethrough.For example, in one embodiment, at least a portion of waveguides 442 cancomprise TE_(xy) waveguides having a generally rectangularcross-section, while, in another embodiment, at least a portion ofwaveguides 442 can comprise TM_(ab) waveguides having generally circularcross-sections. According to one embodiment of the present invention,circular cross-section waveguides can have a diameter of at least about8 inches, at least about 10 inches, at least about 12 inches, at leastabout 24 inches, at least about 36 inches, or at least about 40 inches.In another embodiment, rectangular cross-section waveguides can have ashort dimension of at least about 1 inch, at least about 2 inches, atleast about 3 inches and/or no more than about 6 inches, no more thanabout 5 inches, or no more than about 4 inches, while the long dimensioncan be at least about 6 inches, at least about 10 inches, at least about12 inches, at least about 18 inches and/or no more than about 50 inches,no more than about 35 inches, or no more than about 24 inches.

As schematically illustrated in FIG. 5, microwave distribution system440 can comprise one or more mode conversion segments 446 operable tochange the mode of the microwave energy passing therethrough. Forexample, mode converter 446 can comprise a TM_(ab)-to-TE_(xy) modeconverter for changing the mode of at least a portion of the microwaveenergy from a TM_(ab) to a TE_(xy) mode. In another embodiment, modeconversion segment 446 can comprise a TE_(xy)-to-TM_(ab) mode converterfor receiving TM_(ab) mode energy and converting and dischargingmicrowave energy in a TE_(xy) mode. The values for a, b, x, and y can bewithin the ranges described previously. Microwave distribution system440 can comprise any number of mode converters 446 and, in oneembodiment, can include at least 1, at least 2, at least 3, or at least4 mode converters positioned at various locations within microwavedistribution system 440.

Turning again to FIG. 5, microwave distribution system 440 can compriseone or more microwave launchers 444 for receiving microwave energy fromgenerator 422 via waveguides 442 and emitting or discharging at least aportion of the microwave energy into the interior of microwave heater430. As used herein, the terms “microwave launcher” or “launcher” refersto any device capable of emitting microwave energy into the interior ofa microwave heater. The microwave distribution systems according tovarious embodiments of the present invention can employ at least 1, atleast 2, at least 3, at least 4, at least 5, at least 6, at least 8, atleast 10, and/or no more than 100, no more than 50, or no more than 25microwave launchers. Microwave launchers can be any suitable shapeand/or size and can be constructed of any materials, including, forexample, selected carbon steels, stainless steels, nickel alloys,aluminum alloys, and copper alloys. In one embodiment wherein microwavedistribution system 440 comprises two or more microwave launchers, eachlauncher can be made of the same material, while, in another embodiment,two or more launchers can be made of different materials.

In operation, microwave energy generated by one or more microwavegenerators 422 can be optionally routed or directed to one or modeconverters 446 (if present) via waveguides 442. Thereafter, themicrowave energy in waveguides 442 can be optionally split into two ormore separate microwave portions (e.g., at least three portions as shownin FIG. 5) before being directed to one or more microwave launchers,illustrated as launchers 444 a-c in FIG. 5. Microwave launchers 444 a-ccan be partially or entirely disposed within microwave heater 430 andcan be operable to introduce or emit at least a portion of the microwaveenergy passed thereto into the interior of heater 430 via one or morespaced launch locations, thereby heating and/or drying the objects,articles, or load disposed therein, including, for example, one or morebundles of wood. Specific configurations and details regarding variousembodiments of microwave heating systems will now be discussed in detailbelow.

Turning now to FIGS. 8-10, several embodiments of microwave heatingsystems configured according to the present invention are provided.Although described as being configured to receive and heat a bundle ofwood, it should be understood that the microwave heating systemsdescribed below can be suitable for use in any of the other processesand systems described previously, as well as any system or processwherein microwave heating is used. Further, it should be understoodthat, although described with reference to a particular figure orembodiment, all elements and components described below may be suitablefor use in any microwave heating system configured according to one ormore embodiments of the present invention.

Turning now to FIGS. 8 a and 8 b, one embodiment of a microwave heatingsystem 720 is illustrated as comprising a microwave heater 730 and amicrowave distribution system 740 for delivering microwave energy from amicrowave generator (not shown) to heater 730. An optional vacuum system(not shown) can be operable in various embodiments to reduce thepressure in the interior of microwave heater 730 to, for example, nomore than about 550 torr, no more than about 450 torr, no more thanabout 350 torr, no more than about 300 torr, no more than about 250torr, no more than about 200 torr, no more than about 150 torr, no morethan about 100 torr, no more than about 75 torr and/or no more thanabout 10 millitorr (10⁻³ torr), no more than about 5 millitorr, no morethan about 2 millitorr, no more than about 1 millitorr, no more thanabout 0.5 millitorr, or no more than about 0.1 millitorr. Severalfeatures of one or more embodiments of microwave heating system 720 willbe discussed in detail below.

Turning now to FIG. 8 a, microwave distribution system 740 isillustrated as comprising an elongated waveguide launcher 760 that is atleast partially, and may be entirely, disposed within the interior ofmicrowave heater 730. As shown in FIG. 8 a, elongated waveguide launcher760 can extend substantially horizontally within the interior ofmicrowave heater 730. As used herein, the term “substantiallyhorizontally” means within about 10° of horizontal. In one embodiment,the ratio of the length of elongated waveguide launcher 760 to the totallength of the interior space of microwave heater 730 can be, forexample, at least about 0.3:1, at least about 0.5:1, at least about0.75:1, or at least about 0.90:1. In one embodiment, elongated waveguidelauncher that extends substantially horizontally 760 can be locatedtoward the upper or lower half of the interior volume of microwaveheater 730 and may be at least partially or entirely vertically disposedabove the heater entrance door 738 and an optional heater exit door (notshown) that, when present, is disposed on a generally opposite end ofmicrowave heater 730. As used herein, the terms “upper” and “lower”volume refer to regions located in the upper vertical or lower verticalportion of the internal volume of the vessel. In one embodiment,elongated waveguide launcher 760 can be, for example entirely disposedwithin the uppermost one-third, one-fourth, or one-fifth of the interiorvolume of microwave heater 730, while, in another embodiment, elongatedwaveguide launcher 760 can be, for example disposed within the lowermostone-third, one-fourth, or one-fifth of the total interior volume ofmicrowave heater 730. To measure the “uppermost” or “lowermost”fractional portions of the total interior volume described above, theportion of the vessel cross-section extending from the respectiveuppermost or lowermost wall of the vessel toward the central axis ofelongation for the desired portion (e.g., one-third, one-fourth, orone-fifth) of the cross-section can be extended along the central axisof elongation to thereby define the “uppermost” or “lowermost”fractional volumes of the internal vessel space.

As shown in FIG. 8 a, microwave heater 730, which can be configured toreceive and heat a bundle of wood, comprises a heater entrance door 738,which can optionally comprise a choke (not shown), configured to allow abundle of wood 702 to be introduced into a bundle receiving space 739.Although illustrated as being in direct contact, it should be understoodthat bundle 702 can also comprise one or more spacers or “stickers”disposed between the boards. In one embodiment (not shown), microwaveheater 730 can also comprise an optional heater exit door 739 positionedon the opposite end of microwave heater 730 from heater entrance door738. When microwave heater 730 comprises a separate heater exit door739, bundle 702 can optionally be loaded via entrance door 738, passedthrough microwave heater 730 and unloaded via the exit door 739, ratherthan being both loaded and unloaded through heater entrance door 738.The reference to “entrance” and “exit” doors in this embodiment is notlimiting, and bundle 702 can optionally be loaded via door 739, passedthrough microwave heater 730 and unloaded via door 738. Further, inanother embodiment, bundle 702 can be both loaded (inserted) andunloaded (removed) from entrance door 738 when, for example, optionalexit door 739 is not present. In one embodiment, elongated waveguidelauncher 760 can be positioned in microwave heater 730 substantiallybelow (not shown) or above bundle 702 such that, as bundle 702 is passedinto, out of, and/or through the interior of heater 730, elongatedlauncher does not have to be moved, removed, retracted, or otherwiserepositioned.

Referring now to FIG. 8 b, a partial detailed isometric view ofelongated waveguide launcher 760 is provided. In one embodiment,elongated waveguide launcher 760 can be substantially hollow andcomprise one or more sidewalls. The one or more sidewalls can beconfigured in a variety of ways such that elongated waveguide launcher760 can have a variety of cross-sectional shapes. For example, in oneembodiment, elongated waveguide launcher 760 can have a single sidewalldefining a substantially circular or elliptical cross-sectional shape.In another embodiment, as shown in FIG. 8 b, elongated waveguidelauncher 760 can comprise four substantially planar side walls 764 a-darranged to give launcher 760 a generally rectangular transverse (or, inanother embodiment, square) cross-sectional configuration. Elongatedwaveguide launcher 760 can be configured to propagate and/or emitmicrowave energy in any suitable mode, including TE_(xy) and/or TM_(ab)modes, as discussed in detail previously. According to one embodiment,elongated waveguide launcher 760 can comprise a elongated TE_(xy)launcher and, in one embodiment, can be implemented with commerciallyavailable rectangular waveguide sizes, such as WR284, WR430, or WR340.The specific dimensions of elongated waveguide launcher 760 can be anysuitable dimensions and, in one embodiment, may be custom fabricatedaccording to the description provided in U.S. application Ser. Nos.11/524,239 and 11/254,261, each incorporated herein by reference to theextent not inconsistent with the present disclosure.

As illustrated in FIG. 8 b, the one or more sidewalls of elongatedwaveguide launcher 760 can define a plurality of launch openings fordischarging or emitting microwave energy into the interior of microwaveheater 730. Although depicted in FIG. 8 b as defining a plurality ofelongated slots 767 a-e having a generally rectangular shape withrounded ends, launch openings 767 a-e can be of any suitable shape. Eachof elongated slots 767 a-e can define a length, designated as “L” inFIG. 8 b, and a width, designated as “W” in FIG. 8 b. In one embodiment,the length-to-width (L:W) ratio of elongated slots 767 a-e can be, forexample, at least about 2:1, at least about 3:1, at least about 4:1, orat least about 5:1. In addition, as shown in FIG. 8 b, elongated slots767 a-e can be oriented at various angles with respect to thehorizontal. In one embodiment, elongated slots 767 a-e can extend at anangle relative to the horizontal of, for example, at least about 10°, atleast about 20°, at least about 30° and/or, for example, no more thanabout 80°, no more than about 70°, or no more than about 60°. In oneembodiment, each of elongated slots 767 a-e can have equal shapes,sizes, and/or orientations. In one embodiment, the shapes, sizes, and/ororientations of individual elongated slots 767 a-e can differ. Changesto the shape, size, and/or orientation of elongated slots 767 a-e canimpact the distribution of energy emitted from elongated waveguidelauncher 760. Although shown as being uncovered in the embodimentillustrated in FIG. 8 b, one or more launch openings 767 can besubstantially covered by one or more covering structures (not shown)adjacent to the launch openings that are operable to prevent the flow offluids into and out of openings 767, but that allow the discharge ofmicrowave energy therefrom.

As shown in FIG. 8 b, one or more of launch openings 767 a-e can be atleast partially, or entirely, defined by one or more sidewalls 764 a-dof elongated waveguide launcher 760. In one embodiment, at least about50 percent, at least about 75 percent, at least about 85 percent, or atleast about 90 percent, for example, of the thickness of launch openings767 a-e can be defined by one or more sidewalls 764 a-d. According tothe embodiment illustrated in FIG. 8 b, launch openings 767 a-e can beat least partially, or entirely, defined by two substantially uprightsidewalls 764 a,c. As used herein, the term “substantially upright”means within 30° of vertical. Sidewalls 764 a-d of elongated launcher760 can be relatively thick in one embodiment, while, in other oneembodiment, sidewalls 764 a-d can be relatively thin. For example, theaverage thickness, designated as x in FIG. 8 b, of sidewalls 764 a-d canbe at least about 1/32 (0.03125) inches, at least about ⅛ (0.125)inches, at least about 3/16 (0.1875) inches and/or, for example, no morethan about ½ (0.5) inches, no more than about ¼ (0.25) inches, no morethan about 3/16 (0.1875) inches, or no more than about ⅛ (0.125) inches.According to one embodiment wherein one or more side walls of elongatedwaveguide launcher 760 are relatively thin, elongated waveguide launcher760 can emit microwave energy into the interior of microwave heater 730with a microwave launch efficiency of at least about 50 percent, atleast about 75 percent, at least about 85 percent, at least about 90percent, or at least about 95 percent. As used herein, the term“microwave launch efficiency” can be defined by converting the result ofthe following equation to a percentage: (total energy introduced intothe launcher−total energy discharged from all of the openings of thelauncher)÷(total energy introduced into the launcher).

Launch openings 767 a-e can be arranged according to any suitableconfiguration or arrangement along elongated waveguide launcher 760. Inone embodiment illustrated in FIG. 8 b, launch openings 767 a-e caninclude a first set of launch openings (e.g., launch openings 767 a,b)disposed on one side of launcher 760 and a second set of launch openings(e.g., launch openings 767 c-e) disposed on another, generally oppositeside of elongated waveguide launcher 760. According to one embodiment,first and second sets of launch openings can be axially staggered fromeach other, such that corresponding openings (e.g., openings 767 a,c,shown as launch pair or opening pair 780 a, and openings 767 b,d, shownas launch or opening pair 780 b) are not axially aligned with oneanother. Although illustrated in FIG. 8 b as having only two launchopening pairs 780 a,b, it should be understood that any desired numberof launch opening pairs can be utilized.

According to one embodiment, each launch pair 780 a,b includes onelaunch opening disposed on one side of elongated waveguide launcher 760(e.g., opening 767 a of pair 780 a and opening 767 b of pair 780 b bothdisposed on side wall 764 a) and another launch opening disposed on theopposite side of launcher 760 (e.g., opening 767 c of pair 780 a andopening 767 d of pair 780 b both disposed on side wall 764 c in FIG. 8b). In one embodiment, the openings 767 a,c and 767 b,d disposed onopposite sides of elongated waveguide launcher 760 can be axiallyaligned, while, in another embodiment, the oppositely-spaced openings767 a,c and 767 b,d can form a plurality of “near neighbor” pairs (e.g.,launch pairs 780 a,b comprise “near neighbor” openings 767 a,c and 767b,d, respectively). In one embodiment, for example, when an odd numberof launch openings is used, one or more single launch openings may standalone without forming a pair with any other opening. In one embodiment,the stand-alone opening may be an end opening, such as end opening 767 eshown in FIG. 8 b.

According to one embodiment wherein pairs 780 a,b comprise near neighborpairs of openings, at least one of the launch openings 767 a-d of launchopening pairs 780 a,b can be configured so as to cancel at least aportion of the microwave energy reflected back into the interior spaceof waveguide 760 as generated by one or more of the other launchopenings 767 a-d of the near-neighbor pairs 780 a,b. For example,microwave energy reflections caused by opening 767 a of pair 780 a canbe at least partially, substantially, or nearly entirely cancelled bythe configuration of the other opening 767 b of pair 780 a. In a similarmanner, the microwave energy reflections caused by opening 767 c of pair780 b can be at least partially, substantially, or nearly entirelycancelled by the configuration of the other opening 767 d of pair 780 b.

Furthermore, in one embodiment when launch openings 767 a-d are arrangedin near neighbor pairs, the total amount of energy transferred from eachof launch opening 767 a-d of opening pairs 780 a,b into the interior ofmicrowave heater 730 can be equal to a fraction of the total amount ofmicrowave energy introduced into launcher 760. For example, in oneembodiment wherein the launcher comprises N paired launch openings and asingle end opening, the fraction of microwave energy emitted from eachpair of launch openings (and/or the unpaired or single end opening) canbe expressed by the following formula: 1/(N+1). Thus, according to oneembodiment illustrated in FIG. 8 b wherein N=2, the total amount ofenergy emitted by each of pairs 780 a,b can be equal to 1/(2+1) or ⅓ ofthe total energy introduced into elongated waveguide launcher 760.Similarly, in such embodiment the energy emitted from an unpaired launchopening (e.g., single end opening 767 e in FIG. 8 b) can be expressed bythe formula 1/(N+1). Thus, in the embodiment shown in FIG. 8 b, launchopening 767 e can also emit approximately ⅓ of the total energyintroduced into elongated waveguide launcher 760.

Another embodiment of a microwave heating system 820 is provided inFIGS. 9 a-h. As shown in FIG. 9 a, microwave heating system 820comprises a microwave heater 820 and a microwave distribution system 840operable to transport microwave energy from a microwave generator (notshown) to heater 820. In one embodiment, microwave heating system 820can also comprise a vacuum system (not shown) for reducing the pressurein microwave heater 830 below atmospheric pressure. As shown in FIG. 9a, microwave heater 830 can include a heater entrance door 838 forintroducing a bundle of wood (or other load) into the interior of heater830. Optionally, microwave heater 830 can comprise a heater exit door(not shown in FIG. 9 a) disposed on the generally opposite end of heater830 from heater entrance door 838. In addition, microwave heater 830 cancomprise a plurality of spaced launch openings, such as thoseillustrated as 841 a,b in FIG. 9 a, located at various positions alongone or more external side walls 831 of microwave heater 830. Launchopenings 841 a,b can be operable to accommodate one or more componentsof microwave distribution system 840, thereby facilitating thetransmission of microwave energy into microwave heater 830. Additionaldetails regarding microwave distribution system 840 will now bediscussed in further detail with regard to FIGS. 9 b-h.

Turning FIG. 9 b, a top partial cutaway view of microwave heater 830 isprovided, particularly illustrating a plurality of microwave launchers844 a-d directly or indirectly coupled to opposite sidewalls 831 a,b ofmicrowave heater 830. As used herein, the term “indirectly coupled”refers to one or more intermediate pieces of equipment used to at leastpartially connect one or more launchers to the vessel. Launchers 844 a-dcan be operable to emit microwave energy into the interior of microwaveheater 830 via one or more open outlets 845 a-d, as shown in FIG. 9 b.Although illustrated in FIG. 9 b as comprising four launchers 844 a-d,it should be understood that microwave heater 830 can comprise anydesired number of launchers. In one embodiment (not shown), microwaveheater 830 can comprise two additional launchers axially positioned tothe left of launchers 844 a,b in FIG. 9 b and/or to the right oflaunchers 844 c,d. The additional launchers (not shown) can be facing inthe same direction and/or in different directions. For example, in oneembodiment shown in FIG. 9 b, launchers 844 a-d are shown as facing inopposite directions. Further, in one embodiment (not shown), microwaveheater 830 can comprise four additional launchers, arranged in ananalogous manner as launchers 844 a-d, illustrated in FIG. 9 b, asdescribed further below.

Microwave launchers 844 can be positioned along, within, or proximatemicrowave heater 830 according to any suitable configuration. In oneembodiment, microwave launchers 844 can be configured to comprise twopairs of launchers. The individual launchers within the pair can belocated on generally the same side (e.g., the pair comprising launchers844 a and 844 d and the other pair comprising launcher 844 b and 844 c)or on generally opposite sides (e.g., the pair comprising microwavelaunchers 844 a and 844 b and the other pair comprising 844 c and 844 d)of microwave heater 830.

As used herein, the term “generally opposite sides” or “opposite sides”refers to two launchers positioned such that the angle of radialalignment defined therebetween is in the range of from at least about90° to about 180°. The “angle of radial alignment (β),” is defined asthe angle formed between two straight lines drawn from the center ofeach launcher to the central axis of elongation of the vessel. Forexample, FIG. 9 c shows exemplary launchers 845 and 846 a, defining anangle of radial alignment, β₁, therebetween. The angle of radialalignment between two launchers positioned on generally opposite sidesof a vessel can be at least about 120°, at least about 150°, at leastabout 165° and/or no more than about 180° or approximately 180°. In oneembodiment, two launchers can be positioned on generally oppositesidewalls, as generally depicted in FIG. 9 b, while, in anotherembodiment, two oppositely disposed launchers can be positioned at ornear the vertical top and bottom of the heater (not shown).

In one embodiment wherein one or more pairs launchers include individuallaunchers located on generally opposite sides of a microwave heater(e.g., launchers 844 b and 844 a or launchers 844 c and 844 d in FIG. 9b), the individual launchers within the pairs can also be axiallyaligned with one another. As used herein, the term “axially aligned”refers to two launchers defining an angle of axial alignmenttherebetween in the range of from 0° to 45°. As used herein, the “angleof axial alignment” can be defined by the angle formed between theshortest straight lines drawn between the centers of each launcher (thatalso intersects the axis of elongation of the vessel) and a line drawnperpendicular to the axis of elongation. In FIG. 9 d, the angle of axialalignment, α, is formed between line 850, which is drawn between thecenters of exemplary launchers 845 and 846, and line 852, which isperpendicular to the axis of elongation 835 a. In one embodiment,axially aligned launchers can define an angle of axial alignment of atleast about 0° and/or, for example, no more than about 30° or no morethan about 15°.

In another embodiment, individual launchers within a pair can be locatedon generally the same side of a microwave heater. As used herein, theterm “generally the same side” or “same side” refers to two launchershaving an angle of radial alignment, β, in the range of from at least orequal to 0° to about 90°. Exemplary launchers 845 and 846 b in FIG. 9 care located on generally the same side of the microwave heater, as theangle of radial alignment defined therebetween (e.g., β₂) is no morethan about 90°. In one embodiment, two launchers disposed on the sameside of a microwave heater can define an angle of radial alignment of atleast about 0° and/or no more than about 60°, no more than about 30°,and no more than about 15°, or approximately 0°.

In one embodiment wherein one or more pairs of launchers includeindividual launchers located on generally the same side of a microwaveheater (e.g., launchers 844 a and 844 d or launchers 844 b and 844 c inFIG. 9 b), the individual launchers within the pairs can also be axiallyadjacent to one another. As used herein, the term “axially adjacent”refers to two or more launchers positioned on the same side of amicrowave heater such that no other launchers on that side are disposedbetween the axially adjacent launchers. According to one embodimentwherein a microwave distribution system comprises two or more pairs ofoppositely positioned microwave launchers, one launcher from the firstpair is disposed on generally the same side as one launcher from thesecond pair, thereby creating an axially adjacent pair of launchers.

As illustrated in FIG. 9 b, each of microwave launchers 844 a-d candefine a respective open outlet 845 a-d for emitting microwave energyinto the interior of microwave heater 830. Open outlets can bepositioned to emit energy into the interior of microwave heater 830 inany suitable pattern or direction. For example, in one embodiment shownin FIG. 9 b, open outlets of axially adjacent launchers (e.g., outlets845 a,d of launchers 844 a,d and outlets 845 b,c of launchers 844 b,c)can be oriented to face each other in a direction substantially parallelto the external sidewall to which the launchers are coupled (e.g.,sidewall 831 a for launchers 844 a,d and sidewall 831 b for launchers844 b,c), thereby discharging microwave energy in that generaldirection. As used herein, the term “substantially parallel” meanswithin about 10° of parallel. In one embodiment, at least one of openoutlets 845 a-d can be oriented to discharge energy substantiallyparallel to the axis of elongation of microwave heater 830, designatedas line 835 in FIG. 9 b. According to one embodiment, at least one ofopen outlets 845 a-d can be oriented toward an axial midpoint of heater830. As used herein, the “axial midpoint” of a vessel is defined by aplane that is orthogonal to axis of elongation 835 and intersects themidpoint 839 of the axis of elongation 835 as shown in FIG. 9 b. In oneembodiment, each of open outlets 845 a-d are oriented toward the axialmid-point of heater 830 such that the open outlet 845 a,b of front-sidelaunchers 844 a,b substantially face towards open outlets 845 c,d ofback-side launchers 844 c,d, as depicted in FIG. 9 b.

According to one embodiment, in operation, microwave energy produced byone or more microwave generators (not shown) can be transported viawaveguides 842 a-d to launchers 844 a-d, which emit the energy into theinterior of microwave heater 830. Although not illustrated in FIG. 9 b,any number or configuration of microwave generators can be used toproduce microwave energy for use in microwave heating system 820. In oneembodiment, a single generator can be used to supply energy to heater830 via waveguides 842 a-d and launchers 844, while, in anotherembodiment, heating system 820 can include two or more generators.According to another embodiment, a network of one or more microwavegenerators can be utilized such that microwave energy is emitted from atleast one, at least two, at least three, or all four of microwavelaunchers 844 a-d at substantially the same time. In one embodiment, oneor more launchers 844 a-d can be coupled to a single generator and theenergy from the generator can be allocated amongst the launchers usingone or more microwave switches. In another embodiment, one or more oflaunchers 844 a-d can have a singly-dedicated generator, such that atleast about 75 percent, at least about 90 percent, or substantially allof the microwave energy produced by that generator is routed to a singlelauncher. Additional details regarding specific embodiments of microwavegenerators, waveguides, and launchers and the operation thereof areprovided shortly, with respect to FIGS. 11 a and 11 b.

The microwave energy propagated by waveguide segments 842 a-d can be inany suitable mode, including, for example, a TM_(ab) mode and/or aTE_(xy) mode, wherein a, b, x, and y have values as previously defined.In one embodiment, waveguide segments 842 a-d each comprise TE_(xy)waveguide segments, with segments 842 a and 842 d configured topenetrate sidewall 831 a and segments 842 b and 842 c configured topenetrate sidewall 831 b and extend radially into the interior ofmicrowave heater 830, toward the axis of elongation 835, as shown inFIG. 9 b.

According to one embodiment of the present invention, the mode of themicrowave energy propagated through waveguide segments 842 a-d can bechanged prior to (or simultaneously with) being emitted into theinterior of microwave heater 830. For example, in one embodiment,TE_(xy) mode energy produced by the microwave generator (not shown inFIG. 9 b) can be emitted into microwave energy as TM_(ab) mode energyafter passing through one or more mode converting segments, representedin FIG. 9 b as mode converters 850 a-d. Mode converters can be of anysuitable size and shape and any suitable number of mode converters canbe used in microwave distribution system 840. In one embodiment, one ormore mode converters 850 a-d can be disposed outside of the interiorspace (volume) of microwave heater 830, while, in another embodiment,mode converters 850 a-d can be partially, or entirely, disposed withinthe interior of microwave heater 830. Mode converters 850 a-d can belocated in or near sidewalls 831 a,b or, as illustrated in FIG. 9 b, canbe spaced from external sidewalls 831 a,b of microwave heater 830.

According to one embodiment wherein mode converters 850 a-d arepartially or entirely disposed within heater 830, the microwave energycan initially enter the microwave heater in a TE_(xy) mode and,subsequently, at least a portion of the energy can be converted suchthat at least a portion of the energy emitted from launchers 844 a-dinto the interior of microwave heater 830 can be in a TM_(ab) mode. Inone embodiment, waveguide segments 842 a-d can comprise TE_(xy)waveguide segments operable to transmit microwave energy from thegenerator to heater 830 in a TE_(xy) mode. In one embodiment, at least aportion of TE_(xy) waveguide segments 842 a-d can be integrated intolaunchers 844 a-d as depicted shown in FIG. 9 b. As the energy passesfrom waveguide segments 842 a-d through mode converters 850 a-d, theenergy is converted to a TM_(ab) mode. Subsequently, the TM_(ab) modeenergy exiting mode converters 850 a-d can then pass through arespective TM_(ab) waveguide segment 843 a-d, illustrated in FIG. 9 b asbeing entirely disposed within the interior of microwave heater 830 andspaced from the sidewalls 833 thereof, before being discharged intoheater 830 via TM_(ab) open outlets 845 a-d.

According to another embodiment depicted in FIG. 9 e, microwave heatingsystem 820 can comprise one or more reflectors 890 a-d positioned nearthe open outlets 845 a-d and operable to reflect or disperse microwaveenergy emitted from launchers 844 a-d into microwave heater 830. In oneembodiment, the reflectors can be fixed or stationary reflectors, suchthat energy is reflected or dispersed while the position of thereflector does not change. In another embodiment illustrated in FIG. 9e, one or more of reflectors 890 can be a movable reflector operable tochange position in order to reflect or disperse microwave energy intomicrowave heater 830. Each movable reflector 890 a-d in FIG. 9 epresents a respective reflecting surface 891 a-d for reflecting ordispersing energy emitted from microwave launchers 844 a-d. As shown inFIG. 9 e, each reflecting surface can be spaced from external side walls831 a,b and can be positioned such that one or more of the respectivelaunch openings 845 a-d of launchers 844 a-d face toward theirrespective reflective surfaces 891 a-d which, in turn, are positioned tocontact, direct, or reflect at least a portion of the microwave energyfrom launch openings 845 a-d. In one embodiment, at least a portion of,or substantially all of, the microwave energy emitted from microwavelaunchers 844 a-d can at least partially contact and can be leastpartially reflected or dispersed by respective reflector surfaces 891a-d. In one embodiment, one or more of reflecting surfaces 891 a-d canbe oriented to face a direction that is substantially parallel thedirection of elongation of external side walls 831 a,b.

In one embodiment, reflector surfaces 891 a-d can be substantiallyplanar, while, in other embodiment, one or more reflector surfaces 891a-d can be non-planar. For example, in one embodiment, one or morenon-planar reflector surfaces 891 a-d can define a curvature asillustrated by embodiment depicted in FIG. 9 h. Reflector surfaces 891a-d can be smooth or can one or more convexities. As used herein, theterm “convexity” refers to a region of a reflector that is surfaceoperable to disperse, rather than reflect, energy therefrom. In oneembodiment, a convexity can have a generally convex shape, asillustrated by the examples of convexities 893 a,b shown in FIGS. 9 fand 9 g. In another embodiment, a convexity can have a generally concaveshape, such as, for example, a dimple or other similar indentation.

According to one embodiment of the present invention, one or morereflectors 890 a-d can be movable reflectors. Movable reflectors can beany reflectors operable to change position. In one embodiment, movablereflectors 890 a-b can be oscillating reflectors capable of moving in adesignated pattern, such as, for example, a generally up-and-downpattern or a pattern of rotation about an axis. In one embodiment,movable reflectors can be randomly movable reflectors operable to movein any of a variety of random and/or unplanned movements.

Movable reflectors 890 a-d can be movably coupled to microwave heater830 according to any suitable method. For example, in one embodimentillustrated in FIG. 9 i, microwave heater 830 can comprise a reflectordriver system (or actuator) 899 for movable reflector 890 within theinterior space of heater 830. As shown in FIG. 9 i, reflector driversystem 899 can comprise one or more support arms 892, which fastenablycouple reflector 890 to an oscillating shaft 893. In order to causeshaft 893 to rotate and thereby move reflector 890 in an in-an-outpattern, as generally indicated by arrow 880, a motor 898 can turn awheel 896 to which a linear shaft 895 can be coupled in a generallyoff-center manner. As indicated by arrow 881, shaft 895 can move in agenerally up-and-down manner as wheel 896 turns, thereby causing a leverarm 894 to rotate shaft 893 about pivot axis 897, as generally indicatedby arrow 882. As a result, reflector 890 can move as generally indicatedby arrow 880 and can be operable to reflect or to disperse at least aportion of the microwave energy emitted from discharge opening 845 ofmicrowave reflector 844 in a pattern determined, at least in part, bythe movement of reflector 890.

Yet another embodiment of a microwave heating system 920 is shown inFIGS. 10 a-f. As illustrated in one embodiment FIG. 10 a, a microwaveheater 930 comprises a heater entrance door 938 for loading a bundle ofwood 902 into the interior of heater 930 and a heater exit door 939 forremoving bundle 902 from microwave heater 930. Although illustrated inFIG. 10 a as including separate entrance and exit doors 938, 939, itshould be understood that microwave heater 930 can, in anotherembodiment, include only a single door for both loading and unloadingbundle of wood 902 from the interior of microwave heater 930. In theembodiment shown in FIG. 10 a, heater entrance and exit doors 938, 939can be located on generally opposite ends of microwave heater 930 suchthat bundle 902 can be generally passed through heater 930 via atransport mechanism, such as, for example, a cart (not shown). Inaddition, microwave heating system 920 can comprise an optional vacuumsystem (not shown) for controlling the pressure in heater 930.

As shown in FIG. 10 a, microwave heating system 920 can include amicrowave distribution system 940 comprising a plurality of spacedlaunch openings 941 a-d defined in an external sidewall 931 of microwaveheater 930. Each launch opening 941 can be operable to receive amicrowave launcher (not shown) for emitting energy into the interior ofmicrowave heater 930. Microwave launchers can be at least partly, orentirely, disposed within the interior of microwave heater 930. Specificembodiments of one or more types of microwave launchers will bediscussed in more detail shortly.

According to one embodiment, microwave energy produced by a microwavegenerator (not shown) can be transmitted in a TE_(xy) mode throughwaveguide segments 942 a-d prior to passing through externalTE_(xy)-to-TM_(ab) mode converters 950 a-d, which convert the energypassing therethrough to a TM_(ab) mode. The resulting TM_(ab) modemicrowave energy can then exit mode converters 950 a-d via respectivewaveguide segments 942 e-h, as illustrated in FIG. 10 a. Thereafter, atleast a portion of the microwave energy in TM_(ab) waveguide segments942 e-h can be passed through respective barrier assemblies 970 a-dprior to entering microwave heater 930 via TM_(ab) waveguide segments942 i-l. As used herein, the term “barrier assembly” can refer to anydevice operable to fluidly isolating the microwave heater from anexternal environment, while still permitting the passage of microwaveenergy therethough. For example, in one embodiment shown in FIG. 10 a,respective barrier assemblies 970 a-d can each comprise at least onesealed window member 972 a-d, which can be permeable to microwaveenergy, but provides a desired degree fluid isolation between eachupstream 942 e-h TM_(ab) waveguide segment and each of downstream 942i-l TM_(ab) waveguide segments. As used herein, the term “sealed windowmember” refers to a window member configured in a manner that it willprovide sufficient fluid isolation between the two spaces on either sideof the window member to allow maintaining a pressure differential acrosssuch window member. Additional details regarding specific embodiments ofbarrier assemblies 970 a-d will now be discussed in detail, with respectto FIG. 10 b.

Barrier assemblies configured according to one embodiment of the presentinvention minimize or eliminate arcing, even at high energy throughputsand/or low operating pressures. According to one embodiment of thepresent invention, each barrier assembly 970 a-d can permit energypassage at a rate of at least about 5 kW, at least about 30 kW, at leastabout 50 kW, at least about 60 kW, at least about 65 kW, at least about75 kW, at least about 100 kW, at least about 150 kW, at least about 200kW, at least about 250 kW, at least about 350 kW, at least about 400 kW,at least about 500 kW, at least about 600 kW, at least about 750 kW, orat least about 1,000 kW and/or not more than about 2,500 kW, not morethan about 1,500 kW, or not more than about 1,000 kW through itsrespective window member 972 a-d, while the pressure in microwave heater930 can be no more than about 550 torr, no more than about 450 torr, nomore than about 350 torr, no more than about 250 torr, no more thanabout 200 torr, no more than about 150 torr, no more than about 100torr, or no more than about 75 torr. In one embodiment, the pressure inmicrowave heater can be no more than about 10 millitorr, no more thanabout 5 millitorr, no more than about 2 millitorr, no more than about 1millitorr, no more than about 0.5 millitorr, or no more than about 0.1millitorr. In one embodiment, the microwave energy passed throughbarrier assemblies 970 a-d can be introduced such that theelectromagnetic field is maintained lower than the threshold of arcingto thereby prevent or minimize arcing in barrier assemblies 970 a-d.

Turning now to FIG. 10 b, an axial cross-sectional view of a barrierassembly 970 is provided. Barrier assembly 970 comprises a first sealedwindow member 972 a and an optional second sealed window member 972 bdisposed within a barrier housing 973. When present, second sealedwindow member 972 b can be operable to cooperate with first sealedwindow member 972 a to provide a desired level of fluid isolationbetween the upstream (e.g., entry) and downstream (e.g., exit) TM_(ab)waveguide segments 975 a,b while permitting the passage of at least aportion of the microwave energy from first TM_(ab) waveguide segment 975a to second TM_(ab) waveguide segment 975 b. According to oneembodiment, first and second TM_(ab) waveguide segments 975 a,b can havecircularly cylindrical cross-sections. In one embodiment, waveguidesegments 975 a,b can be two ends of a single continuous waveguide, inwhich barrier assembly 970 can be disposed, while, in anotherembodiment, waveguide segments can be two separate waveguide portions orcomponents suitably fastened or coupled to either side of barrierassembly 970.

As shown in FIG. 10 b, barrier housing 973 can comprise a first or entrysection 973 a, an optional second or intermediate section 973 b, andthird or exit section 973 c, with first sealed window member 972 adisposed between first and second sections 973 a,b and second sealedwindow member 972 b disposed between second and third sections 973 b,c.According to one embodiment, the pressure of each of first, second, andthird segments 973 a,b,c can be different. For example, in oneembodiment, the pressure of first segment 973 a can be greater than thepressure of second segment 973 b, which can be greater than the pressureof third segment 973 c. Each of first, second, and third sections 973a-c of barrier housing 973 can be held together by any suitablefastening device (not shown), such as, for example screws, bolts, andthe like. Further, barrier assemblies 970 a-d can also comprise one ormore impedance transformers, which alter the impedance of the microwaveradiation. An example is illustrated as impedance transforming diameterstep changes 974 a,b in the embodiment shown in FIG. 10 b, formaximizing energy transfer from the microwave generator (not shown) tothe load in the microwave heater (not shown). In one embodiment,impedance transforming diameter step changes 974 a,b can be located nearat least one of sealed window members 972,b, while, in anotherembodiment, step changes 974 a,b can be located near or at leastpartially defined by the entry and/or exit TM_(ab) waveguides 975 a,b.

As illustrated in FIGS. 10 a and 10 b, sealed window members 972 a,b cancomprise one or more discs. Each disc can be constructed of any materialwith a suitable degree of corrosion resistance, strength, impermeabilityto fluids, and permeability to microwave energy. Examples of suitablematerials can include, but are not limited to, aluminum oxide, magnesiumoxide, silicon dioxide, beryllium oxide, boron nitride, mullite, and/orpolymeric compounds such as TEFLON. According to one embodiment, theloss tangent of the disc can be no more than about 2×10⁻⁴, no more thanabout 1×10⁻⁴, no more than about 7.5×10⁻⁵, or no more than about 5×10⁻⁵.

The discs can have any suitable cross-section. In one embodiments discscan have a cross-section compatible with the cross-section of theadjoining waveguides 975 a,b. In one embodiment, the discs can have asubstantially circular cross-section and can have a thickness,designated in FIG. 10 b as “x”, equal to at least about ⅛, at leastabout ¼, at least about ½ and/or no more than about 1, no more thanabout ¾, or no more than about ½ of the length of the predominantwavelength of the microwave energy passing through barrier assembly 970.The diameter of the discs can be at least about 50 percent, at leastabout 60 percent, at least about 75 percent, at least about 90 percentand/or no more than about 95 percent, no more than about 85 percent, nomore than about 70 percent, or no more than about 60 percent of thediameter of one or more adjoining waveguides 975 a,b.

Each disc of sealed window members 972 a-d can be operably coupled torespective barrier assembly 970 a-d in any suitable fashion. In oneembodiment, each of sealed window members 972 a-d can comprise one ormore sealing devices flexibly coupled to barrier housing 973 and/orsealed window members 972 a,b. As used herein, the term “flexiblycoupled” means fastened, attached, or otherwise arranged such that themembers are held in place without directly contacting one or more rigidstructures. For example, in one embodiment shown in FIG. 10 b, barrierassembly 970 can comprise a plurality of resilient rings 982 a,b and 984a,b compressed between various segments 973 a-c of and operable toflexibly couple sealed window members 972 a,b into barrier housing 973.

According to one embodiment, each respective upstream 982 a,b anddownstream 984 a,b resilient rings can be operable to adequately preventor limit fluid flow between first and second 973 a,b and/or second andthird 973 b,c sections of barrier assembly 970. For example, whensubjected to a helium leak test according to procedure B1 entitled“Spraying Testing” described in the document entitled “Helium LeakDetection Techniques” published by Alcatel Vacuum Technology using aVarian Model No. 938-41 detector, the fluid leak rate of sealed windowmembers 972 a-d and/or barrier assemblies 970 a-d can be no more thanabout 10⁻² torr liters/sec, no more than about 10⁻⁴ torr liters/sec, orno more than about 10⁻⁸ torr liters/sec. In addition, each of sealedwindow members 972 a,b can individually be operable to maintain orwithstand a pressure differential across sealed window members 972 a,band/or barrier assembly 970 in amounts such as at least about 0.25 atm,at least about 0.5 atm, at least about 0.75 atm, at least about 0.90atm, at least about 1 atm, or at least about 1.5 atm without outbreaking, cracking, shattering, or otherwise failing.

Turning now to FIG. 10 c, a cross-sectional microwave heating system 920is provided. The microwave heating system depicted in FIG. 10 c includesa microwave distribution system 940 comprising at least one pair ofmicrowave launchers (e.g., launchers 944 a and 944 h) disposed ongenerally opposite sides of a microwave heater 930. Although shown asincluding a single pair of launchers in FIG. 10 c, it should beunderstood that microwave distribution system 940 can further compriseone or more additional pairs of similarly (or somewhat differently)configured microwave launchers having, in some embodiments, one launcherfrom each pair disposed on generally opposite sides of microwave heater930. Further, in another embodiment (not shown in FIG. 10 c), microwavedistribution system 940 may comprise two or more rows vertically-spacedmicrowave launchers positioned on the generally same side of microwaveheater 930. In one embodiment, each side of microwave heater 930 caninclude two or more vertically-spaced rows of launchers, such that onelauncher from each oppositely-disposed pair may be located at a highervertical elevation than one launcher from another oppositely-disposedpair. For example, in one embodiment, launchers 944 a and/or 944 h couldbe positioned at a slightly higher vertical elevation than depicted inFIG. 10 c and another launcher pair could be positioned such that one ofthe two launchers would be positioned on the same side of microwaveheater 930, but at a generally lower vertical elevation than launcher944 a, and the other launcher would be positioned on the same side ofmicrowave heater 930, but at a generally lower vertical elevation thanlauncher 944 h. Furthermore, although shown as split launchers 944 a,h,the vertically-spaced launchers, in one embodiment, could be any type(or any combination of types) of microwave launchers described herein.

As shown in FIG. 10 c, microwave distribution system 940 comprises aplurality of waveguide segments 942 coupled to at least one pair ofmicrowave launchers 944 a,h. For example, as shown in the embodiment inFIG. 10 c, launcher 944 a can be coupled to waveguide segments 942 a,942 e, and 942 i, while launcher 944 h can be coupled to waveguidesegments 942 x, 942 y, and 942 z operable to deliver microwave energyfrom one or more microwave generators (not shown in FIG. 10 c) to theinterior of microwave heater 930. In one embodiment, microwavedistribution system 940 can include one or more mode converters 947 a-d,as shown in FIG. 10 c, coupled to one or more of waveguide segments 942.According to one embodiment, mode converters 947 a-d can be operable tochange the transmission mode of the microwave energy passingtherethrough from a TE_(xy) mode to a TM_(ab) mode (i.e., aTE_(xy)-to-TM_(ab) mode converter) or from a TM_(ab) mode to a TE_(xy)mode (i.e., a TM_(ab)-to-TE_(xy) mode converter). For example, as shownin FIG. 10 c, mode converters 947 a and 947 c can each be operable toconvert the microwave energy transmitted through waveguides 942 a and942 x from a TE_(xy) mode to a TM_(ab) mode as it passes into waveguides942 e and 942 y. As discussed previously, the values of a, b, x, and ycan be the same or different and can have the values provided above.Optionally, mode converters 947 b and 947 d can be operable to convertthe microwave energy transmitted through waveguides 942 e and 942 i aswell as the energy transmitted through 942 y and 942 z from a TM_(ab)mode to a TE_(xy) mode.

Further, in one embodiment illustrated in FIG. 10 c, at least one ofmode converters 947 a-d can comprise a mode converter splitter operableboth to change the mode of the microwave energy passing therethrough andto split it into two or more separate streams of microwave energy fordischarge into the interior space of the microwave heater. According toone embodiment, second mode converters 947 b and 947 d can each comprisemode converting splitters at least partially disposed within theinterior of microwave heater 930. In another embodiment, second modeconverting splitters 947 b and 947 d can be entirely disposed within theinterior of microwave heater 930 and can each be a part of a splitlauncher 944 a and 944 h, respectively, as illustrated in FIG. 10 c.Additional details regarding split launchers 944 a,h will be discussedshortly.

According to one embodiment of the present invention wherein themicrowave distribution system 940 comprises two or more mode convertersin one or more waveguide segments, the total electrical length betweenthe first and second mode converters, extending through and includingthe electrical length of any barrier assembly (if present) can be equalto a value that is a non-integral number of half-wavelengths of thecompeting mode of microwave energy passing therethrough. As used herein,the term “electrical length” refers to the electrical path oftransmission of the microwave energy, expressed as the number ofwavelengths of the microwave energy required to propagate along a givenpath. In one embodiment wherein the physical transmission path includesone or more different type of transmission media having two or moredifferent dielectric constants, the physical length of the transmissionpath can be shorter than the electrical length. Thus, electrical lengthdepends on a number of factors including, for example, the specificwavelength of microwave energy, the thickness and type (e.g., dielectricconstant) of the transmission medium or media.

According to one embodiment, the total electrical length between thefirst mode converter 947 a,c and the second mode converter 947 b,dextending through and including the total electrical length of theTM_(ab) barrier assembly 970 a,h can be equal to a non-integral numberof half-wavelengths of the competing mode of microwave energy. As usedherein, the term “non-integral” refers to any number that is not a wholenumber. A non-integral half-wavelength, then, may correspond to adistance of n times λ/2, wherein n is any non-integral number. Forexample, the number “2” is a whole number, while the number “2.05” is anon-integral number. Thus, an electrical length corresponding to 2.05times the half-wavelength of the competing mode of microwave energywould be a non-integral number of half-wavelengths of that competingmode.

As used herein, the term “competing mode of microwave energy” refers toany mode of microwave energy propagating along a given path other thanthe desired or target mode of microwave energy intended for propagationalong that path. The competing mode may include a single, most prevalentmode (i.e., the predominant competing mode) or a plurality of different,non-prevalent competing modes. When multiple competing modes arepresent, the total electric length between the first and second modeconverters, extending through and including the electrical length of anybarrier assembly (if present), can be equal to a value that is anon-integral number of half-wavelengths of at least one of the multiplecompeting modes and, in one embodiment, can be equal to a value that isa non-integral number of half-wavelengths of the predominant competingmode.

For example, in one embodiment depicted in FIG. 10 c, first modeconverters 947 a,c comprise TM_(ab) mode converters operable to convertat least a portion of the microwave energy in respective waveguidesegments 942 a and 942 d from a TE_(xy) mode into a TM_(ab) mode inwaveguide segments 942 b and 942 e. However, in practice, at least aportion of the microwave energy may be converted into a mode other thanthe desired mode. Any mode other than the desired mode is generallyreferred to herein as the “competing mode” of microwave energy. In oneembodiment of the present invention wherein the desired mode ofmicrowave energy is a TM_(ab) mode, the competing mode of microwaveenergy may be a TE_(mn) mode, wherein n is 1 and m is an integer between1 and 5. Thus, in one embodiment, the total electrical length of theTM_(ab) waveguides 942 e and 942 i between first and second modeconvertors 947 a and 947 b, extending through and including theelectrical length of barrier assembly 970 a, can be equal to anon-integral number of half-wavelengths of the TE_(mn) mode, wherein nis 1 and m is an integer between 1 and 5. In another embodiment, m canbe 2 or 3.

In one embodiment, selecting physical lengths and properties ofwaveguide segments 942, mode converters 947 a-d, and/or barrierassemblies 970 a,h can minimize energy concentration within barrierassemblies 970 a,h. For example, according to one embodiment, while atleast about 5 kW, at least about 30 kW, at least about 50 kW, at leastabout 60 kW, at least about 65 kW, at least about 75 kW, at least about100 kW, at least about 150 kW, at least about 200 kW, at least about 250kW, at least about 350 kW, at least about 400 kW, at least about 500 kW,at least about 600 kW, at least about 750 kW, or at least about 1,000 kWand/or not more than about 2,500 kW, not more than about 1,500 kW, ornot more than about 1,000 kW of energy can be passed through barrierassemblies 970 a,h, the temperature of at least a portion of at leastone sealed window member within barrier assemblies 970 a,h (not shown inFIG. 10 c) can change by no more than about 10° C., no more than about5° C., no more than about 2° C. or no more than about 1° C. In anotherembodiment, the pressure differential across the at least one sealedwindow member and/or the pressure within microwave heater 930 can bemaintained as described above with similar results.

According to one embodiment illustrated in FIG. 10 c, at least one ofthe individual microwave launchers 944 a,h located on generally oppositesides of and at least partially disposed within the interior ofmicrowave heater 930 can comprise a split launcher defining at least twodischarge openings for emitting microwave energy into the interior ofmicrowave heater 930. Although illustrated as comprising a single pair(e.g., a first split launcher 944 a and a second split launcher 944 h)of launchers in FIG. 10 c, it should be understood that microwave heater930 can comprise any suitable number of launchers or pairs of launchers,as described herein.

One embodiment of a split launcher 944 is depicted in FIG. 10 d. Splitlauncher 944 can comprise a single inlet or openings 951 for receivingmicrowave energy and a single (not shown) or two or more dischargeopenings, or outlets, 945 a,b for emitting microwave energy therefrom.In one embodiment, the ratio of microwave energy inlets to dischargeoutlets for a single split launcher can be 1:1, at least 1:2, at least1:3, or at least 1:4. According to one embodiment, the mode of themicrowave energy introduced into inlet 951 can be the same as the modeof the microwave energy emitted via discharge openings 945 a,b, while,in another embodiment, the modes can be different. For example, in oneembodiment wherein split launcher 944 comprises a mode convertingsplitter 949, the microwave energy introduced into a single inlet of afirst sidewall of a microwave heater can undergo a mode conversion andbe divided into at least two separate microwave energy portions, whichcan subsequently be emitted into the interior of the heater, optionallyin a different mode. For example, in one embodiment shown in FIG. 10 d,split launcher 944 can comprise a TM_(ab) waveguide segment 942, one ortwo or more TE_(xy) waveguide segments 943 a,b and a TM_(ab) to TE_(xy)mode converting splitter 949 disposed therebetween. In operation,microwave energy in a TM_(ab) mode introduced via waveguide segment 942passes through mode converting splitter 949 before being discharged,simultaneously or nearly simultaneously, in one or two or more separatefractions of microwave energy from respective outlets 945 a,b ofwaveguides 943 a,b in a TE_(xy) mode.

When launcher 944 comprises a single discharge opening, mode convertingsplitter 949 can simply be a mode converter 949 (not a splitter) forchanging the mode of the microwave energy passing therethrough. Forexample, in one embodiment wherein launcher 944 comprises a singledischarge opening (not shown in FIG. 10 d), launcher 944 can comprise asingle TM_(ab) waveguide segment, a single TE_(xy) waveguide segment,and a TM_(ab)-to-TE_(xy) mode converter 949 disposed therebetween. Themode converter can be located outside, partially inside, or completelyinside the interior of the microwave heater. In operation, microwaveenergy in a TM_(ab) mode introduced via the inlet waveguide segment canpass through mode converter 949 before being discharged in a TE_(xy)mode. The discharge opening of the single-opening launcher can beoriented at any suitable angle with respect to the horizontal or can besubstantially parallel to the horizontal. In one embodiment, the energydischarged from the single-opening launcher can be oriented from thehorizontal by an angle of at least about 20°, at least about 30°, atleast about 45°, or at least about 60° and/or not more than about 100°,not more than about 90°, or not more than about 80°.

When multiple discharge openings are present, each of discharge openings945 a,b of split launcher 944 can be oriented from each other such thatthe paths of microwave energy discharged therefrom define a relativeangle of discharge, Θ, as shown in FIG. 10 d. In one embodiment, therelative angle of discharge between the paths of microwave energydischarge openings 945 a,b can be at least about 5°, at least about 15°,at least about 30°, at least about 45°, at least about 60°, at leastabout 90°, at least about 115°, at least about 135°, at least about 140°and/or no more than about 180°, no more than about 170°, no more thanabout 165°, no more than about 160°, no more than about 140°, no morethan about 120°, no more than about 100°, or no more than about 90°. Inone embodiment, the orientation of discharge openings 945 a,b can alsobe described with respect to the orientation of the paths of themicrowave energy discharged therefrom relative to the axis of extension948 of TM_(ab) waveguide segment 942. In one embodiment, each ofdischarge openings 945 a,b can be configured to discharge microwaveenergy at respective first and second discharge angles (φ₁ and φ₂) fromthe axis of extension 948 of TM_(ab) waveguide segment 942. In oneembodiment, φ₁ and φ₂, can be approximately equal, as generally depictedin FIG. 10 d, or, in another embodiment, one of the two angles can belarger than the other. In various embodiments, φ₁ and/or φ₂ can be atleast about 5°, at least about 10°, at least about 15°, at least about30°, at least about 35°, at least about 55°, at least about 65°, atleast about 70° and/or no more than about 110°, no more than about 100°,no more than about 95°, no more than about 80°, no more than about 70°,no more than about 60°, or no more than about 40°.

In one embodiment, split launcher 944 can be a vertically-oriented splitlauncher such launcher 944 comprises at least one upward-orienteddischarge opening (e.g., 945 a) configured to emit microwave energy atan upward angle from the horizontal and at least one downward-orienteddischarge opening (e.g., 945 b) configured to emit microwave energy at adownward angle from the horizontal. Although depicted in FIG. 10 c ascomprising vertically-oriented split launchers 944 a,h configured todischarge energy at angles relative to the horizontal, in anotherembodiment, one or more of split launchers 944 a,h of microwave heater930 can be horizontally-oriented, such that the split launcher, asdescribed above, has been are rotated by 90°. In another embodiment, oneor more split launchers 944 a,h can be rotated by an angle between 0°and 90°. In one embodiment (not shown), a microwave heater can includetwo or more vertically-spaced rows of horizontally-oriented splitlaunchers located on one side of the heater and two or morevertically-spaced rows of horizontally-oriented split launchers on theother, generally opposite side of the same heater. According to thisembodiment, the vertically-spaced rows of launchers can comprisesingle-opening launchers, horizontally-oriented split launchers,vertically-oriented split launchers, or any combination thereof.

In one embodiment shown in FIG. 10 c, microwave heater 930 can compriseone or more (or at least two) movable reflectors 990 a-d positioned atvarious locations within microwave heater 930 and configured to rastermicrowave energy emitted from one or more discharge openings 945 a-d ofone or more microwave launchers 944 a,h into the interior of microwaveheater 930. Reflectors 990 a-d can have any suitable configuration, suchas, for example, configurations including one or more of the featurespreviously described with respect to FIGS. 9 f-h. Further, althoughgenerally illustrated as comprising four movable reflectors 990 a-d, itshould be understood that microwave heater 930 can comprise any suitablenumber of movable reflectors. In one embodiment, a microwave heatercomprising n split launchers can comprise at least 2n movablereflectors. In another embodiment, a microwave heater can employ a totalof four movable reflectors, each defining a reflector surface thatextends substantially along the length of microwave heater 930, suchthat two or more axially adjacent launchers “share” one or morereflectors or reflecting surfaces.

Regardless of the specific number of reflectors employed, each reflector990 a-d can be operable to raster at least a portion of the microwaveenergy exiting launchers 944 a,h via discharge openings 945 a-d intomicrowave heater 930 to thereby heat and/or dry at least a portion ofthe bundle or other object, article, or load. As used herein, the term“raster” means to direct, project, or concentrate energy over a certainarea. In contrast to conventional reflecting or dispersing energy,rastering energy involves a greater degree of intentional directing orconcentrating, which can be accomplished by utilizing the quasi-opticalproperties of microwave energy. In contrast to conventional means,rastering does not include use of stationary reflection surfaces orconventional mode stirring devices, such as fans. In one embodiment, themicrowave heater can comprise a plurality of split launcher pairs (e.g.,two or more pairs of launchers), wherein each pair comprises twolaunchers having substantially similar configurations (as describedabove). In one embodiment, one launcher of each pair can be positionedon generally opposite sides or on the same side of the microwave heater,as discussed in detail previously, with respect to FIGS. 9 c and 9 d.According to one embodiment, one or more movable reflectors 990 a-d canbe positioned near (and/or positioned to face) one or more dischargeopenings of each of microwave launchers 944. In one embodiment whereinfirst and second launchers 944 a and 944 h each comprise split microwavelaunchers defining respective upward-oriented discharge openings 945 aand 945 c and respective downward-oriented discharge openings 945 b and945 d, at least one movable reflector can be positioned near one or moreof discharge openings 945 a-d to raster at least a portion of themicrowave energy discharged from split launchers 944 a,h (e.g., two ormore separate TE_(xy) mode microwave portions) into the interior ofmicrowave heater 930. In one embodiment illustrated in FIG. 10 c,microwave heater 930 can comprise at least four movable reflectors, eachdefining a respective reflecting surface and positioned near respectivedischarge openings 945 a-d of split launchers 944 a,h. As illustrated inFIG. 10 c, movable reflectors 990 a-d can be located in the bottom leftquadrant (e.g., reflector 990 a), the top left quadrant (e.g., reflector990 b), the top right quadrant (e.g., reflector 990 c), and the bottomright quadrant (e.g., reflector 990 d) of microwave heater 930. Two ormore of reflectors 990 a-d can also be present when launchers 944 a,hare horizontally-oriented split launchers or single-opening launchers,as described in detail previously.

Movable reflectors 990 a-d can be configured in two vertically-spacedpairs (e.g., reflector 990 a paired with reflector 990 b and reflector990 c paired with reflector 990 d) and/or in two horizontally-spacedpairs (e.g., reflector 990 b paired with reflector 990 c and reflector990 a paired with reflector 990 d). As illustrated in FIG. 10 c, pairsof vertically-spaced reflectors (e.g., reflector pair 990 a,b and 990c,d) can be positioned near split launchers 944 a,h such that onemovable reflector is positioned near each of discharge openings 945 a-dof launchers 944 a,h (e.g., discharge openings 945 a-d face towardsrespective movable reflectors 990 a-d). As depicted in FIG. 10 c,movable reflectors 990 b and 990 c can be positioned at a highervertical elevation than respective movable reflectors 990 a and 990 d,such that split launchers 944 a,h can be vertically positioned betweenvertically-spaced pairs of launchers (e.g., launcher 944 a verticallypositioned between vertically-spaced pair of reflectors 990 a,b andlauncher 944 h vertically positioned between vertically-spaced pair ofreflectors 990 c,d). In one embodiment, movable reflector 990 ispositioned such that reflector surface 991 faces toward an open outletof its corresponding microwave launcher (not shown). In anotherembodiment, one or more movable reflectors 990 a-d can be positioned inalignment with or positioned to face the central axis of elongation ofmicrowave heater 930 (not shown in FIG. 10 c).

Movable reflectors 990 a-d can be directly or indirectly coupled to oneor more side walls of a microwave heater and can be moved or actuated inany suitable fashion. One or more of the reflectors 990 a-d can movealong a pre-programmed (planned) path, or one or more can be caused tomove in a random or non-repeating pattern. When multiple reflectors 990a-d are present, two or more reflectors 990 a-d can have the same orsimilar pattern of movement, in one embodiment, while, in the same oranother embodiment, two or more reflectors 990 a-d can have differentpatterns of movement. According to one embodiment, at least one ofreflectors 990 a-d can move in a generally arcuate-shaped path and canpass through various segments or “regions” of the overall path with acertain speed and/or residence time. The size and number of regions, aswell as the speed with which the reflector moves through each region orthe reflector residence time in each region depend on a variety offactors, such as for example, the size and type of the bundle, the typeof wood, and the preliminary and desired characteristics of the initialand final bundle.

In one embodiment, each of reflectors 990 a-d can be individually drivenor actuated according to one or more embodiments described herein,while, in another embodiment, two or more reflectors can be connected toa common drive mechanism (e.g., rotating shaft to be actuated at thesame time. One example of a drive mechanism for moving a reflector 990using an actuator 960 is shown in FIG. 10 e. Actuator 960 can be alinear actuator having a fixed portion 961 coupled to a sidewall 933 ofthe microwave heater and an extensible portion 963 connected to amovable reflector 990. According to one embodiment illustrated in FIG.10 e, at least part of fixed portion 961 can extend through externalside wall 933 and into a bellows structure 964, thereby sealinglycoupling actuator 960 to side wall 933. In one embodiment, bellowsstructure 964 can be operable to reduce, minimize, or nearly preventfluid flow into or out of the location where actuator 960 extendsthrough side wall 933. As shown in FIG. 10 e, movable reflector 990further comprises a support arm 980 pivotally coupled to side wall 933of the microwave heater. As used herein, the term “pivotally coupled”refers to two or more objects attached, fastened, or otherwiseassociated such that at least one of the objects can generally move orpivot about a fixed point. In operation, a driver 970 moves extensibleportion 963 of linear actuator 960 in an in-and-out type motion, asindicated by arrow 971. Extensible portion 963 of linear actuator 960allows movable reflector 990 to move in a generally arcuate pattern, asindicated by arrow 973. Driver 970 can be controlled in any suitablemanner, including, for example, using one or more programmable automaticcontrol systems (not shown).

According to one embodiment of the present invention, it may beadvantageous to minimize the amount of unoccupied, unobstructed, or openvolume defined within the interior of a microwave heater. As usedherein, the term “total open volume” refers to the total volume of spacewithin the interior of the vessel not occupied by physical obstructionswhen a bundle of wood is not disposed in the vessel. In one embodimentof the present invention, the ratio of the total volume of the bundle ofwood (including spaces between individual pieces of wood) to the totalopen volume of the microwave heater can be at least about 0.20, at leastabout 0.25, at least about 0.30, at least about 0.35. In some of theforegoing embodiments, the ratio is also no more than about 0.75, nomore than about 0.70, or no more than about 0.65.

In one embodiment, the microwave heater can define an unobstructedbundle-receiving space for receiving a bundle of wood. The unobstructedbundle receiving space can also be configured to receive at least aportion of the microwave energy emitted to heat and/or dry one or moreobjects (or bundles) therein. Unobstructed bundle-receiving space ofmicrowave heater 930 is denoted as 951 in FIG. 10 c. As used herein, theterm “unobstructed bundle-receiving space” refers to a space definedwithin the interior of a microwave heater that is capable of receivingand holding a bundle of wood. In one embodiment, the unobstructed bundlereceiving space can define a volume of a similar shape and within about10 percent of the volume occupied by the largest size bundle of woodable to be loaded and/or processed within microwave heater 930. Forexample, if the largest bundle size able to be accommodated by microwaveheater was 1,000 cubic feet, the unoccupied bundle receiving space wouldhave a volume, in one embodiment of about 1,100 cubic feet and a similarshape (e.g., cuboidal) as the bundle processed within heater 930.

The bundle receiving space may be “unobstructed” because it may notinclude any physical obstructions (e.g., waveguides, launchers,reflectors, etc.) disposed therein on a permanent basis. In oneembodiment of the present invention, the microwave heater can comprise acircular cross-sectional shape, while unobstructed bundle-receivingspace 951 can define a cuboidal volume and/or be configured to receive abundle of wood having a cuboidal shape. In one embodiment, the ratio ofthe total open volume of microwave heater 930 to the volume of theunobstructed bundle-receiving space can be at least about 0.20, at leastabout 0.25, at least about 0.30, at least about 0.35. In some of theforegoing embodiments, the ratio is also no more than about 0.75, nomore than about 0.70, or no more than about 0.65.

According to one embodiment, at least a portion of the unobstructedbundle receiving space 951 can be defined between two or more“obstructions,” including, for example, two or more launchers,reflectors, waveguides, or other objects located on the same orgenerally opposite sides of microwave heater 930 that take up physicalspace within the interior volume of the heater. In one embodimentwherein microwave heater 930 comprises two oppositely-disposed doors(e.g., an entrance door 928 and an exit door disposed on generallyopposite ends of microwave heater 930), at least a portion ofunobstructed bundle receiving space 951 can be defined between the twooppositely-disposed doors. In one embodiment illustrated in FIG. 10 c,none of launchers 944 a,h or movable reflectors 990 a-d, which areexamples of obstructions, are disposed within unobstructed bundle space951. In one embodiment wherein at least a portion of the unobstructedbundle receiving space is defined between two or more obstructions(e.g., waveguides, launchers, reflectors, etc.), the minimum clearancebetween the outermost edges of one or more obstructions and theunobstructed bundle-receiving space (and/or the bundle, when present)can be at least about 0.5 inches, at least about 1 inch, at least about2 inches, at least about 6 inches, at least about 8 inches and/or nomore than about 18 inches, no more than about 10 inches, or no more thanabout 8 inches. In one embodiment, one of the obstructions do notphysically contact the bundle when loaded into heater 930.

One or more embodiments of the operation of a microwave heating systemaccording to the present invention will now be described, with generalreference to a process for heating a bundle of wood. However, it shouldbe understood that one or more elements of the heating processesdescribed herein can also be suitable for use in processes for heatingother items, as, for example, those processes described previously.Furthermore, it should be understood that one or more of theabove-described embodiments of microwave heating systems, includingthose discussed with respect to FIGS. 8-10 and variations thereof, canbe operated using at least some, or all, of the operational steps,methods, and/or processes described in detail below.

To initiate heating of a bundle of wood, the wood can first be loadedinto a microwave heater, which can be configured according to one ormore embodiments of the present invention previously described. In oneembodiment, the bundle can have an overall initial weight (e.g., priorto heating) of at least about 100 pounds, at least about 250 pounds, atleast about 375 pounds, or at least 500 pounds prior to heating and/ordrying. Once loaded, the vacuum system, if present, can then be used toreduce the pressure of the heater to no more than about 550 torr, nomore than about 450 torr, no more than about 350 torr, no more thanabout 300 torr, no more than about 250 torr, no more than about 200torr, no more than about 150 torr, no more than about 100 torr, or nomore than about 75 torr.

While maintaining the sub-atmospheric pressure in the microwave heater,one or more microwave generators can then be operated to beginintroducing microwave energy into the interior of the vessel to therebyheat and/or dry at least a portion of the bundle. During theintroduction of microwave energy into the interior of the microwaveheater, the pressure within the vessel can be above, nearly at, or belowatmospheric pressure. According to one embodiment, the pressure of theinterior of the microwave heater during the heating step can be at least350 torr, at least about 450 torr, at least about 650 torr, at leastabout 750 torr, at least about 900 torr, or at least about 1,200 torr,while, in another embodiment, the pressure in microwave heater can be nomore than about 350 torr, no more than about 250 torr, no more thanabout 200 torr, no more than about 150 torr, no more than about 100torr, or no more than about 75 torr. The total generator capacity or therate of energy introduced into the interior of the microwave heaterduring the heating and/or drying of the wood can be at least about 5 kW,at least about 30 kW, at least about 50 kW, at least about 60 kW, atleast about 65 kW, at least about 75 kW, at least about 100 kW, at leastabout 150 kW, at least about 200 kW, at least about 250 kW, at leastabout 350 kW, at least about 400 kW, at least about 500 kW, at leastabout 600 kW, at least about 750 kW, or at least about 1,000 kW and/ornot more than about 2,500 kW, not more than about 1,500 kW, or not morethan about 1,000 kW.

According to one embodiment, the process of heating a bundle of wood cancomprise a plurality of individual sequential heating cycles. Theoverall heating process can comprise at least 2, at least 3, at least 4,at least 5, at least 6 and/or no more than 20, no more than 15, no morethan 12, or no more than 10 individual sequential heating cycles. Eachheating cycle can include the introduction of microwave energy,optionally at sub-atmospheric pressure. In one embodiment, microwaveenergy can be introduced into the microwave heater under a pressure ofnot more than about 350 torr, while, in other one embodiment, thepressure in the microwave heater can be at least about 350 torr.

According to one embodiment, each of the one or more individual heatingcycles can be carried out for (e.g., have a duration of) at least about2 minutes, at least about 5 minutes, at least about 10 minutes, at leastabout 20 minutes, at least about 30 minutes and/or no more than about180 minutes, no more than about 120 minutes, or no more than about 90minutes. Overall, the entire length of the heating process (e.g.,overall cycle time) can be at least about 0.5 hours, at least about 2hours, at least about 5 hours, or at least about 8 hours and/or no morethan about 36 hours, no more than about 30 hours, no more than about 24hours, no more than about 18 hours, no more than about 16 hours, no morethan about 12 hours, no more than about 10 hours, no more than about 8hours, or no more than 6 hours.

In one embodiment, wherein the overall heating process comprises two ormore individual heating cycles, one or more subsequent individualheating cycles can be carried out with a different input rate ofmicrowave energy and/or at a different pressure than the previous cycle.For example, in one embodiment, the subsequent individual heating cyclescan be carried out at a lower input rate of microwave energy and/or at alower pressure than the previous cycle. In another embodiment, one ormore subsequent individual heating cycles can be carried out at a higherinput rate of microwave energy and/or at a higher pressure than theprevious cycle. In yet another embodiment, one or more subsequent cyclescan be carried out at a lower input rate of microwave energy and ahigher pressure or a higher input rate of microwave energy and a lowerpressure than one or more previous individual heating cycles. When theoverall heating process includes two or more individual heating cycles,one or more of the second (or later) cycles may be carried out asdescribed above, according to some embodiments. In other embodiments,two or more cycles can be carried out at the same or nearly the samepressure and/or input rate of microwave energy.

According to one embodiment, the overall heating process can include afirst sequential heating cycle followed by a second heating cycle,wherein the second heating cycle is carried out with a lower input rateof microwave energy than the first heating cycle, a lower pressure thanthe first heating cycle, or both a lower input rate of microwave energyand a lower pressure than the first heating cycle. Further, in oneembodiment when the overall cycle comprises three or more heatingcycles, the input rate of microwave energy and/or pressure of eachsubsequent cycle (other than the first) can be lower than the input rateof microwave energy and/or pressure of the previous cycle. For example,in one embodiment, the nth individual heating cycle can be carried outat a lower input rate of microwave energy, a lower pressure, or both alower input rate of microwave energy and a lower pressure than the(n−1)th individual heating cycle.

During the first individual heating cycle, a first maximum input rate ofmicrowave energy can be introduced into the microwave heater. As usedherein, the term “maximum input rate of microwave energy” refers to thehighest rate at which microwave energy is introduced into the heaterduring a heating cycle. In various embodiments, the maximum input rateof microwave energy introduced during the first individual heating cycle(e.g., the first maximum input rate of microwave energy) can be, forexample at least about 5 kW, at least about 30 kW, at least about 50 kW,at least about 60 kW, at least about 65 kW, at least about 75 kW, atleast about 100 kW, at least about 150 kW, at least about 200 kW, atleast about 250 kW, at least about 350 kW, at least about 400 kW, atleast about 500 kW, at least about 600 kW, at least about 750 kW, or atleast about 1,000 kW and/or, for example, not more than about 2,500 kW,not more than about 1,500 kW, not more than about 1,000 kW, or not morethan 500 kW.

Subsequently, a second individual heating cycle can be carried out suchthat the second maximum input rate at which microwave energy isintroduced into the microwave heater during the second individualheating cycle (e.g., the second maximum input rate of microwave energy)can, in some embodiments, be, for example, at least about 25 percent, atleast about 50 percent, at least about 70 percent and/or, for example,no more than about 98 percent, no more than about 94 percent, or no morethan about 90 percent of the maximum input rate achieved during thefirst heating cycle. Similarly, when the heating process comprises threeor more individual heating cycles, the maximum input rate of microwaveenergy of the nth individual heating cycle (e.g., third or fourth cycle)in one embodiment can be, for example, at least about 25 percent, atleast about 50 percent, at least about 70 percent and/or, for example nomore than about 98 percent, no more than about 94 percent, no more thanabout 90 percent, or no more than about 85 percent of the maximum inputrate during the (n−1)th (e.g., previous) individual heating cycle.

In one embodiment, the second (or subsequent) individual heating cyclecan be carried out at a lower pressure than the first (or previous)individual heating cycle. For example, in one embodiment whereinsub-atmospheric or vacuum pressure is utilized during the heating cycle,the lowest pressure reached during the first heating cycle can be atleast about 250 torr. Subsequently, a second individual heating cyclecan be carried out such that the lowest pressure reached (e.g., highestlevel of vacuum pressure achieved) during the second cycle can, in oneembodiment, for example, be at least about 25 percent, at least about 50percent, at least about 70 percent, at least about 75 percent, at least80 percent and/or in one embodiment, for example, no more than about 98percent, no more than about 94 percent, or no more than about 90 percentof the lowest pressure reached during the first heating cycle.Similarly, when the heating process comprises three or more individualheating cycles, the pressure of the nth individual heating cycle in oneembodiment, for example, can be at least about 25 percent, at leastabout 50 percent, at least about 70 percent, at least about 75 percent,at least 80 percent and/or no more than about 98 percent, no more thanabout 94 percent, no more than about 90 percent of the lowest pressurereached, or no more than 85 percent of the lowest pressure reachedduring the (n−1)th individual heating cycle.

Table 1, below, summarizes broad, intermediate, and narrow ranges forthe microwave energy rate, expressed as a percent of maximum generatoroutput, and the pressure, expressed in torr, for consecutive first,second, third, and nth individual heating cycles, according to oneembodiment of the present invention. As used herein, the term “maximumgenerator output” refers to the maximum combined over the entire arraycumulatively generated by all of the microwave generators within aheating system. In one embodiment, the maximum input rate of microwaveenergy for one or more heating cycles can also be expressed as apercentage of maximum generator output, as shown in Table 1.

TABLE 1 Microwave Energy Rate and Pressures for Individual HeatingCycles Rate of Microwave Energy, % of Max Pressure, torr IndividualInterme- Interme- Cycle No. Broad diate Narrow Broad diate Narrow 160-100% 70-100% 80-100% <250 <200 20-100 2 40-100% 50-95%  60-90%  <250<200 20-100 3 20-80%  25-75%  30-70%  <250 <150 20-100 n 5-60% 10-50% 15-40%  <150 <100 10-75 

According to one embodiment of the present invention, each of the one ormore individual heating cycles can comprise a heating period (e.g., afirst, second, or nth heating period), wherein microwave energy isintroduced into the heater, and an optional resting period (e.g., afirst, second, or nth resting period) wherein a reduced amount orsubstantially no microwave energy is introduced into the heater. Forexample, during the heating period, microwave energy can be introducedinto the microwave heater at an input rate sufficient to heat and/or atleast partially dry at least a portion of the wet or chemical-wet bundleof wood, while, during the resting period, the input rate of microwaveenergy introduced into microwave heater can, in one embodiment, be nomore than about 25 percent, no more than about 10 percent, no more thanabout 5 percent, or no more than about 1 percent of the maximum inputrate of microwave energy introduced during the heating period. In oneembodiment wherein multiple individual heating cycles are employed, eachcycle can include one or more heating periods and one or more restperiods. For example, when two individual sequential heating cycles areutilized, the first individual heating cycle can include at least afirst heating period and a first resting period, while the secondindividual heating cycle can include at least a second heating periodand a second resting period. Alternatively, the second heating periodcan follow the first heating period with no interim resting period.

In one embodiment, each of the heating periods can have, for example, aduration of at least about 5 minutes, at least about 10 minutes, atleast about 15 minutes, at least about 30 minutes and/or, for example,no more than about 60 minutes, no more than about 40 minutes, no morethan about 30 minutes, or no more than about 20 minutes. In oneembodiment, the resting period can have a duration of, for example, atleast about 5 minutes, at least about 10 minutes, or at least about 20minutes and/or, for example, no more than about 90 minutes, no more thanabout 60 minutes, or no more than about 40 minutes. In one embodiment,the ratio of the length of the heating period to the length of theresting period of an individual heating cycle can be for example, atleast about 0.5:1, at least about 1:1, at least about 1.25:1, or atleast 2:1 and/or, for example, no more than about 5:1, no more thanabout 3:1, no more than about 2.5:1, or no more than about 1.5:1.

Microwave energy can be introduced into the microwave heater during eachof the heating periods in any suitable manner. For example, in oneembodiment, microwave energy can be emitted from one or more launchersin a substantially continuous manner throughout the entire duration ofthe heating period. In one embodiment, energy can be emitted from onesingle launcher at a time, while, in another embodiment, energy can beemitted from two or more launchers simultaneously. The amount, timing,duration, coordination, and synchronization of microwave energydischarged from each of the launchers can be controlled using anautomatic control system. When the discharge of energy into themicrowave heater includes switching between two or more launchers, theswitching can also be controlled by the control system, as discussed indetail shortly.

According to one embodiment, energy can be introduced into the microwaveheater such that each heating period can include two or more differentheating modes (also called discharge modes, discharge phases, or heatingphases). In one embodiment, different rates of microwave energy can beemitted from one or more launchers during each heating phase. Forexample, in one embodiment, during a first heating phase, energy can beemitted from a first launcher at a higher rate than is emitted from asecond launcher, while, during a second heating phase, energy can beemitted from the second launcher at a higher rate than from the firstlauncher. According to one embodiment, one or more launchers can emitmicrowave energy into the microwave heater, while one or more launcherscan emit substantially no energy into the microwave heater, therebyfocusing energy onto different locations of the bundle of wood (or otherobject). Each separate heating phase can be carried out for a period(i.e, have a duration) of, for example at least about 2 minutes, atleast about 5 minutes, at least about 12 minutes, at least about 15minutes and/or, for example, no more than about 90 minutes, no more thanabout 60 minutes, no more than about 45 minutes or no more than about 30minutes. An optional resting period of at least about 2 minutes, atleast about 4 minutes, or at least about 6 minutes and/or no more thanabout 15 minutes, no more than about 12 minutes, or no more than about10 minutes can follow one or both separate heating phases.

When the microwave heater comprises four or more launchers, themicrowave distribution system can be configured such that each launcheremits microwave energy into the microwave heater in a separate heatingor discharge phase, depending on the position of one or more microwaveswitches. For example, in one embodiment wherein the microwave heatercomprises a first, second, third, and fourth microwave launcher, two ormore microwave switches (e.g., a first and a second microwave switch)can be configured such that microwave energy can be predominantlyemitted from each launcher in a respective first, second, third, andfourth heating phase. In one embodiment, two or more discharge phasescan be carried out at substantially the same time, while two or moredischarge phases can be prevented from being carried out substantiallythe same time. Additional details regarding operation of microwaveheaters utilizing heating periods that include alternating dischargephases will now be discussed in detail below, with reference to FIGS. 11a and 11 b.

Turning now to FIGS. 11 a and 11 b, schematic top views of a microwaveheating system 1020 configured according to one embodiment of thepresent invention are provided. Microwave heating system 1020 isillustrated as comprising at least four microwave generators 1022 a-dfor producing microwave energy and a microwave distribution system 1040for directing at least a portion of the microwave energy into amicrowave heater 1030. Microwave distribution system 1040 also comprisesa plurality of spaced microwave launchers 1044 a-h (which, in oneembodiment, can comprise one or more split launchers) operable to emitat least a portion of microwave energy into the interior of microwaveheater 1040. Each of microwave launchers 1044 a-h can be operablycoupled to one or more of a plurality of (in this figure, a firstthrough fourth) microwave switches 1046 a-d, as shown in FIGS. 11 a and11 b. Microwave switches 1046 a-d can be operable to route microwaveenergy to one or more of launchers 1044 a-h in any suitable modeincluding, for example, a TM_(ab) mode and/or a TE_(xy) mode, asdiscussed in detail previously. In one embodiment, the energy propagatedthrough microwave distribution system 1040 can change modes at leastonce prior to being discharged into microwave heater 1030. Variousconfigurations and methods of operating microwave heating system 1020according to one or more embodiments of the present invention will nowbe described in detail below, with reference to FIGS. 11 a and 11 b.

Each of microwave switches 1046 a-d can be operable to direct, control,or allocate the flow of microwave energy to each of two or moremicrowave launchers 1044 a-h positioned on generally the same side orgenerally opposite sides of microwave heater 1030. For example, in oneembodiment depicted in FIG. 11 a, each of microwave switches 1046 a-dcan be coupled to a pair of axially adjacent microwave launchers (e.g.,launchers 1044 a and 1044 b, launchers 1044 c and 1044 d, launchers 1044e and 1044 f, and launchers 1044 g and 1044 h), represented as launcherpairs 1050 a-d. In another embodiment illustrated in FIG. 11 b, each ofmicrowave switches 1046 a-d can be coupled to a pair of axially alignedmicrowave launchers (e.g., launchers 1044 a and 1044 h, launchers 1044 band 1044 g, launchers 1044 c and 1044 f, and launchers 1044 d and 1044e), shown as launcher pairs 1050 e-h.

Microwave switches 1046 a-d can be any suitable type of microwave switchand, in one embodiment, can be a rotary microwave switch. A rotarymicrowave switch can include an outer housing, an internal routingelement disposed therein, and an actuator for moving the internalrouting element within the housing. In one embodiment, the internalrouting element can be rotatably coupled to the outer housing and theactuator can be operable to selectively rotate the internal routingelement, relative to the outer housing, to thereby switch or direct thedirection of flow of the microwave energy passing therethrough. Othertypes of suitable microwave switches can also be employed. In oneembodiment, microwave switches 1046 a-d can comprise TE_(xy) switches,while, in another embodiment, microwave switches 1046 a-d can compriseTM_(ab) switches. Any additional suitable components, such as one ormore mode converters, barrier assemblies, or components discussedelsewhere in this application but not shown in FIGS. 11 a and 11 b, canbe located upstream or downstream microwave switches 1046 a-d.

In operation, microwave switches 1046 a-d can be selectively switchablebetween a first heating (or discharge) phase and a second heating (ordischarge) phase. During the first heating phase, more energy can beemitted or discharged from one or more microwave launchers, while lessenergy is emitted from one or more other microwave launchers. Similarly,during the second heating phase, more energy can be emitted ordischarged from one or more other microwave launchers, while less energycan be emitted or discharged from one or more microwave launchers.

In one embodiment, during the first heating phase, each of microwaveswitches 1046 a-d can be configured to route microwave energypredominantly to one or more launchers within a first set of microwavelaunchers (labeled as set of “A” launchers in FIGS. 11 a and 11 b) andnot predominantly to one or more launchers of a second set of microwavelaunchers (labeled as a set of “B” launchers in FIGS. 11 a and 11 b).During the second discharge phase, each of microwave switches 1046 a-dcan be configured to route microwave energy predominantly to one or morelaunchers of the second set (e.g., the “B” launchers) and notpredominantly to one or more launchers of the first set (e.g., the “A”launchers) in each of respective pairs of launchers 1050 a-d and 1050e-h, in FIGS. 11 a and 11 b. As used herein, references to routingmicrowave energy “predominantly” to launcher X and “not predominantly”to launcher Y means that at least about 50 percent of the microwaveenergy received by a switch is routed to launcher X, while no more thanabout 50 percent of the microwave energy received by the switch isrouted to launcher Y. In one embodiment, for example at least about 75percent, at least about 90 percent, at least about 95 percent,substantially all of the energy can be predominantly routed to launcherX, while, for example no more than about 25 percent, no more than about10 percent, no more than about 5 percent or substantially none of theenergy can be routed to launcher Y.

In one embodiment, microwave heating system 1030 can further comprise acontrol system 1060 for controlling the action and configuration ofmicrowave switches 1046 a-d. In one embodiment, control system 1060 canbe operable to configure each of switches 1046 a-d to be in the firstdischarge phase, such that all “A” launchers (e.g., launchers 1044a,c,e,g) emit microwave energy into microwave heater 1030, while all “B”launchers (e.g., launchers 1044 b,d,f,h) emit a smaller amount of, orsubstantially no microwave energy into the interior of microwave heater1030, as illustrated by the respective shaded and un-shaded regions ofmicrowave heater 1030 in FIGS. 11 a and 11 b. Subsequently, controlsystem 1060 can then be operable to configure each of switches 1046 a-dto be in the second discharge phase, such that all “A” launchers (e.g.,launchers 1044 a,c,e,g) emit a smaller amount of, or substantially nomicrowave energy into the interior of microwave heater 1030, while all“B” launchers (e.g., launchers 1044 b,d,f,h) emit microwave energy intothe interior of microwave heater 1030 (not represented in FIGS. 11 a and11 b).

According to one embodiment, control system 1060 can also be operable tocontrol the switching of microwave switches 1046 a-d between the firstand second discharge phases based on a set of predetermined parametersincluding, for example, cycle time, total energy discharged, and thelike. For example, in one embodiment, control system 1060 can beoperable to configure each of microwave switches 1046 a-d into the firstdischarge phase substantially simultaneously, such that microwave energycan be emitted from each of the “A” launchers 1044 a,c,e,g simultaneousfor a period of time. In another embodiment, control system 1060 can beoperable to include a time delay or lag between configuring one or moreswitches 1046 a-d into the first discharge phase. As a result, themicrowave energy emitted from one or more “A” or “B” launchers may bedelayed or staggered, relative to the discharge of energy from one ormore other “A” or “B” launchers. In one embodiment, control system 1060may be configured to allow one or more switches 1046 a-d to be in thefirst discharge phase, while one or more other switches 1046 a-d are inthe second discharge phase, such that microwave energy can be emittedfrom one or more “A” launchers and one or more “B” launcherssimultanously. In one embodiment of the present invention, controlsystem 1060 can also be operable to at least partially preventsimultaneous energy discharge from directly opposed pairs of launchers(e.g., pair 1044 a and 1044 h, pair 1044 b and 1044 g, pair 1044 c and1044 f, pair 1044 d and 1044 e) and/or axially adjacent pairs (e.g.,pair 1044 a and 1044 b, pair 1044 c and 1044 d, pair 1044 e and 1044 f,pair 1044 g and 1044 h).

Heating systems configured and/or operated according to one embodimentof the present invention can be operable to heat an object or load moreefficiently than conventional heating systems. In particular, heatingsystems configured according to various embodiments of the presentinvention can be operable to process large, commercial-scale loads. Inone embodiment, heating systems as described herein can heat a bundle ofwood or other load having a cumulative, pre-heating (or pre-treatment)weight of at least about 100 pounds, at least about 500 pounds, at leastabout 1,000 pounds, at least about 5,000 pounds, or at least about10,000 pounds. In various embodiments, a bundle of wood can be heatedand/or dried such that no more than, for example, about 20 percent, nomore than about 10 percent, no more than about 5 percent, and no morethan about 2 percent of the total volume of wood can reach a temperaturethat does exceed an upper threshold temperature. In the same or otherembodiments, at least about 80 percent, at least about 90 percent, atleast about 95 percent, and at least about 98 percent, for example, ofthe total volume of wood can reach a temperature that does exceed alower threshold temperature. The lower and upper threshold temperaturescan be relatively close to one another and can, for example, be withinabout 110° C., within about 105° C., within about 100° C., within about90° C., within about 75° C., or within about 50° C. of each other. Invarious embodiments, the upper threshold temperature can be at leastabout 190° C., at least about 200° C., or at least about 220° C. and/orno more than about 275° C., no more than about 260° C., no more thanabout 250° C., or no more than about 225° C. In another embodiment, thelower threshold temperature can be at least about 115° C., at leastabout 120° C., at least about 125° C., at least about 130° C. and/or nomore than about 150° C., no more than about 145° C., or no more thanabout 135° C.

According to one embodiment, at least about 80 percent, at least about90 percent, at least about 95 percent, and at least about 98 percent ofthe total volume of the wood can reach a maximum temperature of at leastabout 130° C., at least about 145° C., at least about 150° C., or atleast about 160° C. and/or no more than about 250° C., no more thanabout 240° C., no more than about 225° C., no more than about 210° C.,or no more than about 200° C. As a result, a bundle of wood (optionallya chemical-wet bundle of wood) having an initial (e.g., pre-heating orpre-treatment) weight of at least about 100 pounds, at least about 500pounds, at least about 1,000 pounds, or at least about 5,000 pounds canbe heated in no more than about 48 hours, no more than about 36 hours,no more than about 24 hours, no more than about 18 hours, no more thanabout 16 hours, no more than about 12 hours, no more than about 10hours, no more than about 8 hours, or no more than about 6 hours.

The various aspects of the present invention can be further illustratedand described by the following Examples. It should be understood,however, that these Examples are included merely for purposes ofillustration and are not intended to limit the scope of the invention,unless otherwise specifically indicated.

EXAMPLES Example 1 Microwave Choke

This example illustrates a microwave choke capable of substantiallyminimizing and/or preventing the leakage of energy from the interior ofa microwave heater. A comparative microwave heater that did not includea microwave choke and an inventive microwave heater employing a chokesimilar to the choke illustrated in FIGS. 7 a-h were each modeled usingHFSS™ software (available from Ansys in Canonsburg, Pa.). The electricfield strengths at and near the junction of the door and the vessel bodywere simulated and the average strengths of the resulting electricfields were calculated both within the interior of each vessel (the“interior area”) and for a region just outside the vessel proximate tothe door flange of each vessel (the “flange area”). Table 2, below,summarizes the average field strengths for each of these areas for boththe comparative and inventive microwave heaters.

TABLE 2 Comparison of Average Electric Field Strength for MicrowaveVessels With and Without a Microwave Choke Average Electric Field AreaSimulated Vessel Choke? Strength (kV/cm) Interior No 0.25 to 0.39 FlangeNo 0.25 to 0.39 Interior Yes 0.25 to 0.39 Flange Yes <0.03

As illustrated in Table 2, the average electric field strengths bothinside and outside the comparative heater, which did not employ amicrowave choke, were approximately the same, indicating significantleakage of microwave energy from within the vessel. In contrast, theaverage strength of the electric field outside the inventive microwaveheater, which did employ a microwave choke as described herein, was anorder of magnitude lower than the average strength of the electric fieldwithin the inventive heater, indicating the microwave energy did notleak out, but remained inside the vessel. This is further illustrated bythe visual results of the simulation, presented in FIGS. 12 a and 12 b.

Thus, it was concluded that the use of a microwave choke as describedherein can sufficiently reduce, minimize, or nearly eliminate theleakage of microwave energy from a microwave vessel.

Example 2 Use of Sequential Heating Cycles Utilizing Different Levels ofMicrowave Energy

This example illustrates how the method of applying heat to a bundle ofwood affects the temperature distribution of the heated wood. Severaltrials were conducted that included one or more individual heatingcycles having various durations, pressures, and/or energy levels todetermine the impact on the temperature of the bundle, as well as thequantity of wood scorched, during the heating cycle.

A microwave heating system similar to the system illustrated in FIGS. 9a, 9 b, and 9 e was constructed and included a FERRITE 75 kW 915 MHzmicrowave generator (commercially available from Ferrite MicrowaveTechnologies, Inc. in Nashua, N.H.) coupled to a vacuum microwave heatervia a series of TE₁₀ waveguides. Three rotary microwave switches wereconfigured to selectively route microwave energy from the generator toone of four microwave launchers located in the interior of the microwaveheater. Each launcher was designed to receive energy in a TE₁₀ mode, butincluded a mode converter disposed within the interior of the vessel forconverting the energy to a TM₀₁ mode before being emitted into theheater. The vacuum heater, which had a diameter of 6.5 feet and anoverall length of 8 feet, included a single door on one end for loadingand unloading the wood. The system also included a mechanical, dry(e.g., non-oil sealed) vacuum pump (commercially available from EdwardsLimited in Tewksbury, Mass.) for controlling the pressure within theheater as desired during the heating step.

For each of trial Runs A-H, six planks of acetylated Radiata pine havingnominal dimensions of 1 inch by 6 inches by 8 feet were equipped withfiber optic temperature sensors placed into holes drilled at the centerpoint of each board. The sensor-equipped boards were placed in row 13 ofa stickered bundle that included a total of 156 boards of acetylatedRadiata pine arranged in 26 layers. The bundle was then fastenedtogether and loaded into the vacuum heater. During each run A-H, thebundle was exposed to different heating and/or pressure profiles. Foreach run, the peak average and peak maximum fiber optic temperatures,the weight of the bundle before and after heating (to calculateevaporative loss), and the total energy input were measured for eachcycle. Key characteristics of each bundle and specifics of each heatingprofile are summarized in Tables 3a and 3b, below.

TABLE 3a Bundle Properties and Individual Heating Profiles for Runs A-HBundle Properties Overall Cycle Data Avg. Dry Total Power EnergyMoisture Weight Pressure Input Density (kW/ Run Content (%) (lb) (torr)(kW-hr) lb dry wood) A 2.55 1553 350 26.2 0.0094 B 2.04 1833 350 30.70.0107 C 2.18 1528 350 26.0 0.0107 D 2.10 1800 350 30.7 0.0109 E 2.701630 200 37.0 0.0148 F 2.45 1592 200 36.0 0.0155 G 2.72 1566 300 32.00.0125 H 1.95 1836 350 41.3 0.0168

TABLE 3b Bundle Properties and Individual Heating Profiles for Runs A-H(cont'd) First Heating Cycle Second Heating Cycle Energy Energy RateTime Rest Rate Time Rest Run (kW) (min) (min) (kW) (min) (min) A 25 63 —— — — B 25 40 30 22 20 14 C 25 55 50 22 10 — D 25 40 30 22 20  9 E 22 6016 18 50 — F 18 40 20 18 40 28 G 20 40 20 20 34 20 H 25 40 35 20 40 40Third Heating Cycle Fourth Heating Cycle Energy Energy Rate Time RestRate Time Rest Run (kW) (min) (min) (kW) (min) (min) A — — — — B 22 20 —— — — C — — — — — — D 22 20 — — — — E — — — — — — F 12 45 — — — — G 1236 — — — — H 16 28 42 12 20 —

Upon completion of each run, the bundle was removed and each of theboards was visually inspected for signs of scorching, which was definedas quarter-size or larger blackened or burned marks. The evaporative(moisture) loss was calculated by comparing the weight of the bundlebefore and after heating (and the known dry weight of each board). Theenergy density (per pound of dry wood) was calculated based on the totalenergy input and initial weight and moisture content of the wood. Table4, below, summarizes the results of runs A-H, including the average andmaximum peak temperatures achieved during heating and the number ofscorched boards.

TABLE 4 Summary of Results for Runs A-H Results Average Maximum EnergyDensity Peak Temp Peak Temp Scorched Run (kW/lb dry wood) (° C.) (° C.)Boards (#) A 0.0094 116 159 0 B 0.0107 119 161 0 C 0.0107 139 184 7 D0.0109 116 179 0 E 0.0148 136 154 19 F 0.0155 123 137 0 G 0.0125 113 1930 H 0.0168 142 192 10

As shown in Table 4, for similar energy densities (e.g., Runs C and Dand Runs E and F), runs employing more individual cycles conducted atlower energy levels and/or for shorter durations (e.g., Runs D and F)were more likely to avoid scorching than runs employing less individualcycles conducted at higher energy levels and/or for longer durations(e.g., Runs C and E). Further, as illustrated by Run H, even runsconducted with multiple cycles having reduced energy levels can resultin scorching if the energy level and/or duration of initial cycles areconducted at a high energy level and/or for a long duration. Thus, itwas concluded that the number and duration of the individual cycleswithin an overall heating cycle, as well as the level of energy and/orpressure of each of the individual cycles, has an impact on the averageand maximum peak temperature of the wood, as well as the number ofboards scorched during the heating cycle.

Example 3 Determination of Energy Distribution Profile within a Bundle

This example provides actual data obtained from a pilot-scale microwaveheater used to heat and/or dry a bundle of acetylated wood. Thermalimages were used to construct an energy distribution profile, which willthen be correlated, in prophetic Example 4, to predict chemical moistureprofiles of wood heated on a commercial scale.

A horizontally-elongated microwave heater similar to the heaterillustrated in FIGS. 10 a, c, d, and e was constructed with an outerdiameter of 12 feet and an overall length of 16 feet. The heaterincluded an entrance door for loading and unloading the bundle from thevessel. Four split microwave launchers similar to those illustrated inFIGS. 10 c and 10 d were arranged in two oppositely-disposed pairs andwere connected to a FERRITE 75 kW 915 MHz microwave generator(commercially available from Ferrite Microwave Technologies, Inc. inNashua, N.H.) via a system of TE₁₀ waveguides. Three microwave switcheswere configured to route energy from the generator to one of the twolaunchers of each pair, as described in detail below.

The microwave heater also included four movable reflectors similar tothose illustrated in FIG. 10 c. Each reflector defined a continuousreflective surface extending substantially along the length of theheater. Each of the four split launchers were vertically positionedbetween a pair of movable reflectors such that the energy emitted fromthe respective upward- and downward-oriented discharge openings of eachsplit launcher was rastered into the interior of the microwave heater bythe reflective surfaces disposed in each of the four quadrants of theinternal volume of the heater. Each reflective surface was rotated alonga generally arcuate path via a shaft, which utilized an external driver.Details regarding the motion of the movable reflectors will be describedin detail shortly.

Approximately 15,000 pounds of acetylated Radiata pine was allowed tomoisture-equilibrate in the ambient atmosphere such that the averagewater content of the wood was about 2-3 weight percent. The wood wasthen bundled into a composite bundle comprising fourindividually-secured stacks (e.g., stacks A-D shown in FIG. 13). Thecomposite bundle, represented as bundle 1304 in FIG. 13, had nominaldimensions of 4 feet wide by 8 feet tall by 16 feet long. Each of stacksA-C had a width of 6 inches, while stack D had a width of 2.5 feet.Composite bundle 1304 was introduced into the microwave heater and thedoor was closed and secured prior to initiating the heating cycle.

First, the microwave switches were configured such that the energy fromthe generator would be routed to two diagonally opposite (e.g.,oppositely-disposed, axially-staggered) launchers at the same time,while the remaining two diagonally opposite launchers remained idle. Thegenerator was then started and set to deliver 75 kW to the firstdiagonally opposite pair of launchers, in a manner similar to the onediscussed previously with respect to launcher set “A” of FIGS. 11 a and11 b. Next, after about 10 minutes, the generator was stopped and themicrowave switches were reconfigured to route energy from the firstactive set of diagonally opposite launchers to the idle set ofdiagonally opposite launchers during the second heating mode. Thegenerator was then restarted at 75 kW and microwave energy was againdischarged into the heater. After another 10 minutes, the generator wasstopped so that the switches could be returned to the originalconfiguration, thereby re-routing energy back to the first pair ofdiagonally opposite launchers. This sequence of alternativelydischarging energy from axially-staggered pairs of launchers continuedin 10-minute increments for a total of 80 minutes (e.g., 100 kW-hr).

During each heating mode, the energy discharged from each of themicrowave launchers was rastered into the interior of the microwaveheater by controlling the motion and position of each of the movablereflectors. A programmable logic controller (PLC) was set to rotate eachreflector, using a servo motor, through various portions (or regions) ofits total arcuate path at various speeds. The top and bottom pairs ofreflectors were programmed to move at the same speed, but the movementof one reflector of each pair was initiated before the other, therebyavoiding both reflectors of the pair moving in synchronized tandem.Table 5 below, summarizes the boundaries (e.g., starting and endingposition) and total length of each of the eight regions of motion, aswell as the reflector speed and time spent in each region (e.g.,residence time) for each of the top and bottom pairs of reflectors,expressed as a percentage of the overall reflector cycle time. Note thatTable 5 summarizes only half of the profile for each reflector; onceeach pair of reflectors moved through regions 1-8 as described below,each reflector then traveled in a reverse pattern, beginning with region8 and moving back to region 1.

TABLE 5 Profile for Movable Reflectors Top Reflectors Bottom ReflectorsStarting Ending Length Length Residence Residence Position Position ofPath of Path Speed Time (% of Speed Time (% of Region (°) (°) (°) (%)(°/s) Cycle) (°/s) Cycle) 1 0.0 0.1 0.1  0.31% 0.07 0.9 0.05 1.0 2 0.14.0 3.9 12.19% 0.10 23.3 0.05 24 3 4.0 8.0 4.0 12.50% 1.82 1.0 1.82 1.34 8.0 12.0 4.0 12.50% 1.82 1.0 1.82 1.3 5 12.0 16.0 4.0 12.50% 1.82 1.01.82 1.3 6 16.0 24.0 8.0 25.00% 1.82 2.0 1.82 2.6 7 24.0 28.0 4.0 12.50%0.25 7.5 0.26 9.5 8 28.0 32.0 4.0 12.50% 0.04 48.0 0.04 59.0

Once the overall heating cycle was complete, the generator was turnedoff and the heated composite bundle was transported to a holding zonewherein a MIKRON 7500 model camera with a wide angle lens was positionedapproximately 10 feet from one of the elongated sides of the heatedbundle. Stack A, the outermost stack of boards shown in FIG. 13, wasremoved from the composite bundle to thereby expose an interior surfaceof stack B, designated as B′ in FIG. 13. The camera recorded thermalimages of surface B′ at a rate of 1 image per every 5 seconds and, afterabout 20 seconds, stack B was removed from the composite bundle. Thecamera then began recording thermal images of an interior surface ofstack C, designated as surface C′ in FIG. 13. After about 20 seconds,stack C was removed from the bundle, thereby exposing the internalsurface of stack D, designated as surface D′ in FIG. 13. The camerarecorded thermal images of surface D′ for about 20 seconds and was thenstopped.

To analyze the composite temperature distribution throughout the volumeof the bundle, pixel-by-pixel temperature data obtained within arepresentative region of interest for each of surfaces B′ through D′ wasimported into a spreadsheet using MikroSpec™ Professional thermalimaging software (version 4.0.5, available from Metrum in Berkshire,UK). A cumulative frequency histogram, incorporating thermal dataobtained from all interior surfaces B′ through D′ of the compositebundle is shown in FIG. 14.

As shown in FIG. 14, less than 20 percent of the volume of the bundlehad a temperature below 42° C. or above 52° C. When correlated to abundle of dried, acetylated wood, this type of energy distributionresults in the predicted chemical moisture content profile, described inprophetic Example 4.

Example 4 (Prophetic): Calculation of Chemical Moisture Content Profilewithin an Acetylated Bundle

This prophetic example uses the experimental energy distribution dataobtained in Example A to predict the chemical moisture profile (e.g.,amount and distribution of one or more heat removable chemicals withinthe total volume) of acetylated wood heated and/or dried in acommercial-scale microwave heating system configured similarly to thesystem described previously in Example 3.

A bundle of acetylated wood, having dimensions of approximately 101inches tall by 52 inches wide by 16 feet long is loaded into a microwaveheater having an internal diameter of 11 feet, 7 inches and aflange-to-flange length of 17 feet. The pressurizable heater includes anoppositely-disposed entrance and exit opening, each sealable with a fulldiameter dished door. The total internal volume of the heater is 2605cubic feet, and the ratio of the total volume of the bundle of wood tothe total open (e.g., unoccupied) volume in the microwave heater is0.29:1. Prior to heating in the microwave heater, the bundle has a“chemical moisture content” (i.e., an amount of one or moreheat-vaporizable chemicals including, for example, acetic acid, aceticanhydride, and combinations thereof) of approximately 10-15 weightpercent.

During heating of the bundle, microwave energy is introduced into themicrowave heater in a similar manner as previously described in Example3. In addition, a vacuum system is used to maintain the internalpressure of the heater at 60 torr. After 80 minutes, the microwavegenerator is turned off, the bundle is removed, and thermal images ofinterior surfaces of the bundle are taken in the manner previouslydescribed in Example 3. The predicted temperature distribution resultingfrom the cumulative thermal data is provided in FIG. 15.

As shown in FIG. 15, the projected temperature distribution for theacetylated bundle of wood has a mean peak temperature of 165° C., andless than 0.3 percent of the total volume of the bundle has atemperature below 115° C. or above 235° C. According topreviously-obtained empirical data correlating wood temperature tochemical moisture content, the temperature distribution in FIG. 15predicts a chemical moisture content profile as summarized in Table 6,for a dried bundle of acetylated wood processed as described above.

TABLE 6 Projected Chemical Moisture Content Profile for Dried AcetylatedWood Percent of Bundle Predicted Moisture Temperature Volume Content T <115° C. 0.3% ~2 wt % moisture 115° C. < T < 135° C. 2.2% ~1 wt %moisture T > 235° C. 0.3% Scorched 115° C. < T < 235° C. 99.4% Dried135° C. < T < 235° C. 97.2% Dried

The overall objective of heating and/or drying the acetylated wood is toremove residual acetylation chemicals (e.g., by minimizing the chemicalmoisture content of the dried bundle), while not over-drying orscorching the treated wood. As shown in Table 6, less than 0.3 percentof the total volume of the acetylated bundle is under-dried (e.g., has amoisture content of 2 weight percent or more) or subjected to scorching(e.g., has an average temperature greater than 235° C.). In addition,less than 2.2 percent of the total volume of the bundle has a moisturecontent of 1 percent or more. Thus, at least 97.2 (and up to 99.4)percent of the total volume of the acetylated bundle is heated and driedto a chemical moisture content of less than 1-2 weight percent, whilesimultaneously minimizing the amount of scorched wood.

The preferred forms of the invention described above are to be used asillustration only, and should not be used in a limiting sense tointerpret the scope of the present invention. Obvious modifications tothe exemplary one embodiment, set forth above, could be readily made bythose skilled in the art without departing from the spirit of thepresent invention.

The inventors hereby state their intent to rely on the Doctrine ofEquivalents to determine and assess the reasonably fair scope of thepresent invention as pertains to any apparatus not materially departingfrom but outside the literal scope of the invention as set forth in thefollowing claims.

1. A system for producing chemically-modified, dried, and/orthermally-modified wood, said system comprising: a microwave heatercomprising a vessel body and a door for selectively permitting andblocking passage of a bundle of wood into and out of the interior ofsaid microwave heater, wherein said door and said vessel body presentrespective door-side and body-side sealing surfaces that directly orindirectly form a fluid seal between said door and said vessel body whensaid door is closed, wherein said door and said vessel bodycooperatively form at least a portion of a microwave choke effective toinhibit leakage of microwave energy out of said microwave heater betweensaid door and said vessel body when said door is closed, wherein saidmicrowave choke comprises a first radially-extending choke cavity, asecond radially-extending choke cavity, and a radially-extending chokeguidewall disposed at least partly between said first and said secondchoke cavities when said door is closed, wherein at least a portion ofsaid second choke cavity extends alongside at least a portion of saidfirst choke cavity when said door is closed.
 2. The system of claim 1,wherein a relative extension angle is defined between the direction ofextension of said first choke cavity and the direction of extension ofsaid second choke cavity, wherein said relative extension angle is lessthan 60°.
 3. The system of claim 1, wherein at least 40 percent of thetotal length of said second choke cavity extends alongside said firstchoke cavity when said door is closed.
 4. The system of claim 1, whereinsaid first and/or said second choke cavity has a length of at least 2inches.
 5. The system of claim 1, wherein said guidewall comprises aplurality of spaced open-ended gaps disposed circumferentially alongsaid guidewall.
 6. The system of claim 1, wherein said choke comprises aremovable portion removably coupled to said vessel body or said door. 7.The system of claim 1, wherein said microwave heater further comprises aresilient sealing member for fluidly isolating the interior of saidmicrowave heater from the external environment, wherein said sealingmember is compressed against said door-side sealing surface and/or saidbody-side sealing surface when said door is closed.
 8. The system ofclaim 1, further comprising a vacuum system operable to reduce thepressure in said microwave heater to not more than 350 torr, furthercomprising at least one microwave generator for providing microwaveenergy to said microwave heater at a rate of at least 50 kW, whereinsaid microwave heater has an internal volume of at least 100 cubic feet.9. The system of claim 1, further comprising a chemical modificationreactor for chemically modifying at least a portion of said bundle ofwood and a transportation system operable to transport said bundle ofwood from said chemical modification reactor to said microwave heater.10. The system of claim 9, wherein said chemical modification reactor isan acetylation reactor for acetylating at least a portion of said bundleof wood.
 11. A system for producing chemically-modified, dried, and/orthermally-modified wood, said system comprising: a microwave heatercomprising a cylindrical vessel body, a door, and a microwave choke,wherein said microwave heater is configured to receive and heat a bundleof wood, wherein said microwave choke is operable to substantiallyprevent leakage of microwave energy out of said microwave heater betweensaid door and said vessel body when said door is closed, wherein saidmicrowave choke comprises a removable choke portion removably coupled tosaid vessel body or said door.
 12. The system of claim 11, wherein saidremovable choke portion is removably coupled to said door.
 13. Thesystem of claim 11, wherein said removable choke portion comprises aplurality of individually removable choke segments, wherein saidindividually removable choke segments have a generally arcuate shape.14. The system of claim 11, wherein said microwave choke comprises afirst radially-extending choke cavity, a second radially-extending chokecavity, and a radially-extending choke guidewall at least partiallydisposed between said first and second choke cavities when said door isclosed, wherein said removable choke portion comprises said guidewall.15. The system of claim 14, wherein said guidewall comprises a pluralityof spaced open-ended gaps disposed circumferentially along saidguidewall.
 16. The system of claim 11, further comprising a vacuumsystem operable to reduce the pressure in said microwave heater to notmore than 350 torr, further comprising at least one microwave generatorfor providing microwave energy at a rate of at least 50 kW to saidmicrowave heater, and wherein said microwave heater has an internalvolume of at least 100 cubic feet.
 17. The system of claim 11, furthercomprising a chemical modification reactor for chemically modifying atleast a portion of said bundle of wood and a transportation systemoperable to transport said bundle of wood from said chemicalmodification reactor to said microwave heater.
 18. The system of claim17, wherein said chemical modification reactor is an acetylation reactorfor acetylating at least a portion of said bundle of wood.
 19. A processfor producing chemically-modified, dried, and/or thermally-modifiedwood, said process comprising: (a) loading a bundle of wood into amicrowave heater through an open door of said microwave heater; (b)closing said door of said microwave heater to thereby form a fluid sealbetween said door and a vessel body of said microwave heater; (c)maintaining a pressure of not more than 350 torr in said microwaveheater; (d) heating said bundle of wood with microwave energy introducedinto said microwave heater while said vacuum is maintained; and (e)simultaneously with step (d), using a microwave choke to prevent atleast a portion of said microwave energy from exiting said microwaveheater at the junction of said door and said vessel body.
 20. Theprocess of claim 19, wherein substantially no arcing occurs proximatesaid microwave choke during said heating of step (d).
 21. The process ofclaim 20, wherein microwave energy is introduced into said microwaveheater at a rate of at least 50 kW during said heating of step (d),wherein step (c) includes maintaining a pressure of not more than 250torr in said microwave heater.
 22. The process of claim 21, wherein notmore than 50 milliwatts per square meter leak out of said heater throughsaid microwave choke during said heating of step (d).
 23. The process ofclaim 19, wherein microwave energy is introduced into said microwaveheater at a rate of at least 200 kW during said heating of step (d),wherein step (c) includes maintaining a pressure of not more than 100torr in said microwave heater, and wherein not more than 10 milliwattsper square meter of microwave energy leak out of said heater throughsaid microwave choke during said heating of step (d).
 24. The process ofclaim 19, further comprising removing at least a portion of saidmicrowave choke from said door or said vessel body without damaging saiddoor or said vessel body.
 25. The process of claim 19, wherein saidbundle of wood loaded into said microwave heater in step (a) weighs atleast 500 pounds at the time said bundle is loaded.
 26. The process ofclaim 19, wherein at least a portion of said bundle of wood has beenchemically modified prior to said loading of step (a).
 27. The processof claim 19, wherein at least a portion of said bundle of wood has beenacetylated prior to said loading of step (a).
 28. A process forproducing chemically-modified, dried, and/or thermally-modified wood,said process comprising: (a) attaching a removable choke portion to adoor or a vessel body of a microwave heater; (b) heating a bundle ofwood with microwave energy introduced into said microwave heater; and(c) simultaneously with step (b), using a microwave choke to prevent atleast a portion of said microwave energy from exiting said microwaveheater at a junction of said door and said vessel body, wherein saidmicrowave choke comprises said removable choke portion.
 29. The processof claim 28, wherein said removable choke portion comprises a pluralityof individually removable choke segments, wherein said attaching of step(a) comprises separately attaching at least a portion of saidindividually removable choke segments to said door or said vessel body.30. The process of claim 28, further comprising removing and replacingat least part of said removable choke portion with a replacement chokeportion, wherein said removable choke portion comprises a plurality ofindividually removable segments, wherein said at least part of saidremovable choke portion that is removed and replaced comprises less thanall of said removable segments.
 31. The process of claim 28, whereinmicrowave energy is introduced into said microwave heater at a rate ofat least 50 kW during said heating of step (b), wherein said heating ofstep (b) includes maintaining a pressure of not more than 250 torr insaid microwave heater, wherein less that 50 milliwatts per square meterleak out of said heater through said microwave choke during said heatingof step (b), wherein substantially no arcing occurs proximate saidmicrowave choke during said heating of step (b).
 32. The process ofclaim 28, wherein said bundle of wood weighs at least 500 pounds priorto said heating of step (b).
 33. The process of claim 28, wherein atleast a portion of said bundle of wood has been chemically modifiedprior to said heating of step (b).
 34. The process of claim 28, whereinat least a portion of said bundle of wood has been acetylated prior tosaid heating of step (b).